M5-T08: add MQTT, HA Discovery, and Modbus polling config fields

app/config.py

@@ -41,9 +41,21 @@ class Settings(BaseSettings):
     auth_trust_forwarded_for: bool = False
     auth_totp_issuer: str = ""  # defaults to app_name when empty
 
-    # Modbus polling — global kill-switch; T08 will wire this into CONFIG_FIELDS/UI.
+    # Modbus polling — global kill-switch (CONFIG_FIELDS registered in T08).
     modbus_polling_enabled: bool = True
 
+    # MQTT broker connection (T08 wires into CONFIG_FIELDS/UI; T10 builds the client).
+    mqtt_enabled: bool = False
+    mqtt_broker_host: str = ""
+    mqtt_broker_port: int = 1883
+    mqtt_username: str = ""
+    mqtt_password: str = ""
+    mqtt_tls_enabled: bool = False
+
+    # Home Assistant MQTT Discovery (T08 wires into CONFIG_FIELDS/UI; T11 does publishing).
+    ha_discovery_enabled: bool = False
+    ha_discovery_prefix: str = "homeassistant"
+
     model_config = SettingsConfigDict(
         env_file=".env",
         env_file_encoding="utf-8",