Web: rework preset UX

Change the radio preset endpoint from https://api.meshcore.nz/api/v1/config
to https://api.vbart.ru/meshcore-firmware/v1/conf.json, which returns
a flat JSON array of city objects:
  [{"code":"BSK","name":"Biysk","timezone":"...","settings":{...}}, ...]

Adapt preset parsing to the new schema: pass entry.settings through
normalizeRadioConfig() at the map step so invalid or missing settings
fields are silently filtered out via filter(Boolean). radioSignature()
and formatRadioConfig() are simplified to operate directly on already-
normalized numbers, using JS default number-to-string to avoid trailing
zeros (62.5 instead of 62.500, 869 instead of 869.000).

Rework the preset UX:
- Remove the auto-matching logic that highlighted the current radio in
  the dropdown; many cities share identical radio settings so it is
  impossible to reliably determine which preset is active.
  The dropdown now starts at "Load from preset".
- When a preset is selected, preview it in the "Current Radio" field
  (relabelled "Selected radio preset") and show "Click Save to apply".
  If the selected preset matches the current radio settings, the Save
  button is not activated and the UI is left unchanged.
- After a successful apply, set radioSettingsChanged=true and show a
  persistent "reboot required" warning; relabel the field "New radio".
- Disable the Save button (with opacity + cursor feedback) until a
  preset is chosen; savebtn:hover suppressed while disabled.
- Reset the preset dropdown when the radio config is refreshed from
  the device.
- Update placeholder to "Loading..." to match the new display format.
- Remove now-unused "Preset" label row from the Radio Settings card.

src/helpers/web/WebPanelServer.cpp

@@ -436,7 +436,8 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
     .iconbtn { width:44px; padding:12px 0; }
     .placeholder-slot { display:block; width:44px; height:44px; }
     .savebtn { width:100%; background:var(--accent); color:var(--button-text); border:none; }
-    .savebtn:hover { background:var(--accent-hover); }
+    .savebtn:not(:disabled):hover { background:var(--accent-hover); }
+    .savebtn:disabled { opacity:0.45; cursor:not-allowed; }
     .broker-stack { display:grid; grid-template-columns:minmax(0,1fr) minmax(0,2fr); gap:12px; align-items:start; }
     .broker-group { display:grid; gap:8px; align-content:start; }
     .broker-grid { display:grid; grid-template-columns:repeat(3,minmax(0,1fr)); gap:10px; }
@@ -749,13 +750,12 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
         <div class="section-group">
           <h3>Radio Settings</h3>
           <div class="field-card">
-            <label class="label" for="radioPreset">Preset</label>
             <div class="row">
               <div class="field-card">
                 <div>
-                  <label class="label" for="radioCurrent">Current Radio</label>
+                  <label class="label" id="radioCurrentLabel" for="radioCurrent">Current Radio</label>
                   <div class="fieldline">
-                    <input id="radioCurrent" placeholder="915.800 / BW250 / SF10 / CR5" readonly disabled>
+                    <input id="radioCurrent" placeholder="Loading..." readonly disabled>
                     <button id="refreshRadioBtn" class="iconbtn" title="Refresh current radio">&#8635;</button>
                   </div>
                 </div>
@@ -1012,7 +1012,7 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
 
   </main>
   <script>
-    const RADIO_PRESETS_URL = "https://api.meshcore.nz/api/v1/config";
+    const RADIO_PRESETS_URL = "https://api.vbart.ru/meshcore-firmware/v1/conf.json";
     const isStatsPage = window.location.pathname === "/stats";
     const PANEL_TITLE_KEY = "repeater-panel-title";
     let token = sessionStorage.getItem("repeater-token") || "";
@@ -1020,6 +1020,7 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
     let radioPresetEntries = [];
     let currentRadioConfig = null;
     let statsLastFetchedAt = null;
+    let radioSettingsChanged = false;
     const statusEl = document.getElementById("status");
     const replyEl = document.getElementById("reply");
     const themeToggleEl = document.getElementById("themeToggle");
@@ -1179,19 +1180,10 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
       };
     }
     function radioSignature(config) {
-      const normalized = normalizeRadioConfig(config);
-      if (!normalized) return "";
-      return [
-        normalized.frequency.toFixed(3),
-        normalized.bandwidth.toFixed(3),
-        normalized.spreadingFactor,
-        normalized.codingRate
-      ].join("|");
+      return [config.frequency, config.bandwidth, config.spreadingFactor, config.codingRate].join("|");
     }
     function formatRadioConfig(config) {
-      const normalized = normalizeRadioConfig(config);
-      if (!normalized) return "";
-      return `${normalized.frequency.toFixed(3)} / BW${normalized.bandwidth.toFixed(3)} / SF${normalized.spreadingFactor} / CR${normalized.codingRate}`;
+      return `${config.frequency} / BW${config.bandwidth} / SF${config.spreadingFactor} / CR${config.codingRate}`;
     }
     function parseRadioValue(value) {
       const parts = String(value || "").split(",");
@@ -1209,6 +1201,10 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
       el.textContent = message || "";
       el.style.color = isError ? "var(--status-red)" : "var(--text-muted)";
     }
+    function setRadioCurrentLabel(text) {
+      const el = document.getElementById("radioCurrentLabel");
+      el.textContent = text;
+    }
     function setGhostNodeModeStatus(message, isError) {
       const el = document.getElementById("ghostNodeModeStatus");
       if (!el) return;
@@ -1311,30 +1307,20 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
     }
     function syncRadioPresetUi() {
       const currentEl = document.getElementById("radioCurrent");
-      if (currentEl) {
-        currentEl.value = currentRadioConfig ? formatRadioConfig(currentRadioConfig) : "";
+      currentEl.value = currentRadioConfig ? formatRadioConfig(currentRadioConfig) : "";
+      if (radioSettingsChanged) {
+        setRadioCurrentLabel("New radio");
+        setRadioPresetStatus("Radio settings were changed, reboot is required.", true);
+      } else {
+        setRadioCurrentLabel("Current Radio");
+        setRadioPresetStatus("", false);
       }
-      const selectEl = document.getElementById("radioPreset");
       const applyBtn = document.getElementById("applyRadioPresetBtn");
-      if (!selectEl || !applyBtn) return;
-      const currentSig = radioSignature(currentRadioConfig);
-      let matchedIndex = -1;
-      for (let i = 0; i < radioPresetEntries.length; i++) {
-        if (radioSignature(radioPresetEntries[i]) === currentSig) {
-          matchedIndex = i;
-          break;
-        }
-      }
+      if (!applyBtn) return;
       if (!radioPresetEntries.length) {
         applyBtn.disabled = true;
         return;
       }
-      if (matchedIndex >= 0) {
-        selectEl.value = String(matchedIndex);
-        applyBtn.disabled = false;
-        return;
-      }
-      selectEl.value = "";
       applyBtn.disabled = true;
     }
     function toneForPercent(percent, invert) {
@@ -2376,6 +2362,7 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
         setRadioPresetStatus("Current radio config was not recognised.", true);
         return;
       }
+      document.getElementById("radioPreset").value = "";
       currentRadioConfig = parsed;
       setRadioPresetStatus("");
       syncRadioPresetUi();
@@ -2393,9 +2380,7 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
     async function loadRadioPresets() {
       const selectEl = document.getElementById("radioPreset");
       const applyBtn = document.getElementById("applyRadioPresetBtn");
-      if (selectEl) {
-        selectEl.innerHTML = '<option value="">Loading presets...</option>';
-      }
+      selectEl.innerHTML = '<option value="">Loading presets...</option>';
       if (applyBtn) applyBtn.disabled = true;
       setRadioPresetStatus("");
       try {
@@ -2403,20 +2388,14 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
         if (!res.ok) {
           throw new Error("Preset service returned " + res.status);
         }
-        const payload = await res.json();
-        const config = payload && payload.config ? payload.config : {};
-        const suggested = config && config.suggested_radio_settings ? config.suggested_radio_settings : {};
-        const entries = Array.isArray(suggested.entries) ? suggested.entries : [];
-        radioPresetEntries = entries.map((entry) => ({
-          title: String(entry.title || "Unnamed preset"),
-          description: String(entry.description || ""),
-          frequency: formatDecimal(entry.frequency, 3),
-          bandwidth: formatDecimal(entry.bandwidth, 3),
-          spreadingFactor: Number.parseInt(entry.spreading_factor, 10),
-          codingRate: Number.parseInt(entry.coding_rate, 10)
-        })).filter((entry) => radioSignature(entry));
-        if (!selectEl) return;
-        const options = ['<option value="">Custom / current</option>'];
+        const entries = await res.json();
+        if (!Array.isArray(entries)) throw new Error("Unexpected preset format");
+        radioPresetEntries = entries.map((entry) => {
+          const normalized = normalizeRadioConfig(entry.settings);
+          if (!normalized) return null;
+          return { title: `${entry.name} (${entry.code})`, ...normalized };
+        }).filter(Boolean);
+        const options = ['<option value="">Load from preset</option>'];
         for (let i = 0; i < radioPresetEntries.length; i++) {
           const preset = radioPresetEntries[i];
           options.push(`<option value="${i}">${escapeHtml(preset.title)}</option>`);
@@ -2425,9 +2404,7 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
         syncRadioPresetUi();
       } catch (error) {
         radioPresetEntries = [];
-        if (selectEl) {
-          selectEl.innerHTML = '<option value="">Community presets unavailable</option>';
-        }
+        selectEl.innerHTML = '<option value="">Community presets unavailable</option>';
         if (applyBtn) applyBtn.disabled = true;
         setRadioPresetStatus(error && error.message ? error.message : "Unable to load community presets.", true);
       }
@@ -2574,29 +2551,30 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
         return;
       }
       const preset = radioPresetEntries[Number.parseInt(value, 10)];
-      if (!preset) {
+      const isAlreadySet = currentRadioConfig && radioSignature(preset) === radioSignature(currentRadioConfig);
+      if (isAlreadySet) {
         syncRadioPresetUi();
         return;
       }
+      const currentEl = document.getElementById("radioCurrent");
+      currentEl.value = formatRadioConfig(preset);
+      setRadioCurrentLabel("Selected radio preset");
+      setRadioPresetStatus("Click \"Save\" to apply.", false);
       document.getElementById("applyRadioPresetBtn").disabled = false;
     });
     document.getElementById("applyRadioPresetBtn").onclick = async () => {
       const selectEl = document.getElementById("radioPreset");
       const index = Number.parseInt(selectEl.value, 10);
       const preset = radioPresetEntries[index];
-      if (!preset) {
-        setRadioPresetStatus("Select a community preset first.", true);
-        return;
-      }
       const command = `set radio ${preset.frequency},${preset.bandwidth},${preset.spreadingFactor},${preset.codingRate}`;
       const result = await runCommand(command);
       if (!result.ok) {
         setRadioPresetStatus(parseReplyValue(result.text) || "Unable to apply radio preset.", true);
         return;
       }
-      currentRadioConfig = normalizeRadioConfig(preset);
+      currentRadioConfig = preset;
+      radioSettingsChanged = true;
       syncRadioPresetUi();
-      setRadioPresetStatus("Preset saved. Reboot to apply the new radio settings.", false);
     };
     document.getElementById("rebootBtn").onclick = async () => {
       if (confirm("Reboot the repeater now?")) {