Add fault alert functionality for WiFi and MQTT disconnections

Implemented a new fault alert system that broadcasts notifications over LoRa when WiFi or MQTT connections are down for a specified duration. The alerts are configurable via CLI commands, allowing operators to set private PSKs or hashtags for alert channels. Default settings for alert thresholds and intervals are established, and the system ensures that alerts do not spam the public channel. Updated relevant files to integrate this feature into the MyMesh implementations and CLI handling.

examples/simple_room_server/MyMesh.cpp

@@ -675,6 +675,15 @@ MyMesh::MyMesh(mesh::MainBoard &board, mesh::Radio &radio, mesh::MillisecondCloc
   _prefs.gps_interval = 0;
   _prefs.advert_loc_policy = ADVERT_LOC_PREFS;
 
+  // Alert channel defaults (same as repeater; off by default and unconfigured).
+  // Operator must pick `set alert.psk` or `set alert.hashtag` before alerts fire.
+  _prefs.alert_enabled = 0;
+  _prefs.alert_psk_b64[0] = '\0';
+  _prefs.alert_hashtag[0] = '\0';
+  _prefs.alert_wifi_minutes = 30;
+  _prefs.alert_mqtt_minutes = 240;
+  _prefs.alert_min_interval_min = 60;
+
   // bridge defaults (same as repeater)
   _prefs.bridge_enabled = 1;    // enabled
   _prefs.bridge_delay   = 500;  // milliseconds