Shorten MQTT probe timeout to limit web server stalls

src/main.cpp

@@ -13,6 +13,7 @@
 #define PWM_RES 10
 #define MQTT_MANUFACTURER "Baumann Enkataleiptics"
 #define AUTH_USERNAME "admin"
+#define MQTT_PROBE_TIMEOUT_MS 400  // keep short: blocks loop()/handleClient() per reconnect attempt
 
 struct MeterConfig {
   int pin;
@@ -340,7 +341,7 @@ static void mqttLoop() {
     if (now > mqttReconnectAt) {
       Serial.printf("[MQTT] probing %s:%d\n", mqttCfg.host, mqttCfg.port);
       WiFiClient probe;
-      bool reachable = probe.connect(mqttCfg.host, mqttCfg.port, 1500);
+      bool reachable = probe.connect(mqttCfg.host, mqttCfg.port, MQTT_PROBE_TIMEOUT_MS);
       probe.stop();
 
       if (reachable) {