feat(companion-wifi): recovery AP with TCP rescue CLI when WiFi is down

When a companion WiFi device has no WiFi credentials or can't connect for
60s, it broadcasts an 'EastMesh-WiFi' AP (WPA2 password = device pin
zero-padded to 8 digits; open if no pin set) with the rescue CLI on TCP
port 23, so wifi.ssid/pwd can be fixed without a serial cable.

- rescue CLI command handler now writes to any Stream (Serial or the TCP
  rescue client)
- while the AP is up, STA keeps retrying; the AP shuts down automatically
  once the configured network connects
- 'set wifi.ssid/pwd' keeps AP+STA mode during a rescue session so the
  session isn't dropped mid-config
- guard ESP32-only SD/SPI code in ArchiveStorage so non-ESP32 builds of
  the shared helpers get further

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

examples/companion_radio/main.cpp

@@ -111,6 +111,10 @@ void halt() {
 #if defined(ESP32) && defined(WIFI_SSID)
   bool wifi_needs_reconnect = false;
   unsigned long last_wifi_reconnect_attempt = 0;
+  unsigned long last_wifi_connected = 0;
+  #ifndef RECOVERY_AP_TIMEOUT_MS
+    #define RECOVERY_AP_TIMEOUT_MS 60000   // STA not connected this long -> recovery AP
+  #endif
 #endif
 
 void setup() {
@@ -278,5 +282,19 @@ void loop() {
     WiFi.reconnect();
     last_wifi_reconnect_attempt = millis();
   }
+
+  // Recovery AP: broadcast our own SSID (with the rescue CLI on TCP) when STA has no
+  // credentials or hasn't been able to connect, so wifi.ssid/pwd can be fixed in place
+  if (the_mesh.isRecoveryAPActive()) {
+    the_mesh.loopRecoveryAP();
+    if (WiFi.status() == WL_CONNECTED) {
+      the_mesh.stopRecoveryAP();   // STA is up again; back to normal operation
+    }
+  } else if (WiFi.status() == WL_CONNECTED) {
+    last_wifi_connected = millis();
+  } else if (the_mesh.getWifiSSID()[0] == 0 ||
+             millis() - last_wifi_connected > RECOVERY_AP_TIMEOUT_MS) {
+    the_mesh.startRecoveryAP();
+  }
 #endif
 }