Web: clear CLI input after Enter and remove misleading placeholder

The Enter key handler in the CLI panel now awaits runCommand() directly
instead of simulating a button click, and clears the input field once
the command has been dispatched. This makes keyboard-driven use more
comfortable: the field is ready for the next command without manual
clearing.

The placeholder text "get mqtt.status" is removed from the command
input. Its color was nearly identical to regular input text, making the
field appear non-empty even when cleared, which was confusing. The
Quick "get" Commands panel already provides one-click buttons for all
common read-only queries, so the hint was redundant in any case.

The Run button onclick path is intentionally unchanged: the command
stays in the field after execution, allowing fast repeat by clicking
Run again without retyping.

src/helpers/web/WebPanelServer.cpp

@@ -628,7 +628,7 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
 	    <section class="card" id="cliPanel" style="display:none">
       <h2>Run CLI Command</h2>
       <div class="row-command">
-        <input id="command" placeholder="get mqtt.status">
+        <input id="command">
         <button id="runBtn">Run</button>
       </div>
       <p class="panel-copy">Authenticated sessions can run repeater CLI commands here.</p>
@@ -2368,10 +2368,12 @@ const char kWebPanelAppHtml[] PROGMEM = R"HTML(
     const openStats = () => window.location.assign("/stats");
     const openApp = () => window.location.assign("/app");
     document.getElementById("openStatsPanelBtn").onclick = () => openStats();
-    document.getElementById("command").addEventListener("keydown", (event) => {
+    document.getElementById("command").addEventListener("keydown", async (event) => {
       if (event.key === "Enter") {
         event.preventDefault();
-        document.getElementById("runBtn").click();
+        const cmd = document.getElementById("command");
+        await runCommand(cmd.value);
+        cmd.value = "";
       }
     });
 	    document.querySelectorAll("[data-cmd]").forEach((btn) => btn.onclick = () => runCommand(btn.dataset.cmd));