[SYS] Add WiFi reconnect watchdog to self-heal from wedged WiFi stack (#2319)

When the network drops at runtime and the WiFi stack is wedged (e.g. the
ESP32 driver getting stuck after a long uptime, see #2276), the main loop
kept calling wifi_reconnect_bypass() forever with no recovery: the device
stayed stale until a manual reboot. The reboot watchdog only existed in the
ESPWifiManualSetup path, which the default WiFiManager build doesn't compile.

Count consecutive reconnection failures in the runtime loop and ESPRestart(2)
once they exceed maxRetryWatchDog, mirroring the existing manual-setup
watchdog. Gated behind the new WifiReconnectWatchDog flag (default on) so
environments where an unexpected reboot is undesirable can opt out; disabled
for theengs-plug to avoid interrupting the relay state.

Co-authored-by: Claude <noreply@anthropic.com>

main/main.cpp

@@ -2594,6 +2594,13 @@ void loop() {
     THEENGS_LOG_WARNING(F("Network disconnected" CR));
     gatewayState = GatewayState::NTWK_DISCONNECTED;
     if (!wifi_reconnect_bypass()) {
+      failure_number_ntwk++;
+      THEENGS_LOG_WARNING(F("failure_number_ntwk: %d" CR), failure_number_ntwk);
+      // Self-heal from a wedged WiFi stack: if reconnection keeps failing, restart the ESP.
+      // Disabled on environments where an unexpected reboot is undesirable (e.g. a smart plug).
+      if (WifiReconnectWatchDog && failure_number_ntwk > maxRetryWatchDog) {
+        ESPRestart(2);
+      }
       sleep();
     } else {
       gatewayState = GatewayState::NTWK_CONNECTED;