M4-T02: add exponential login back-off service and wire into login endpoint

app/config.py

@@ -37,6 +37,8 @@ class Settings(BaseSettings):
     auth_session_cookie_name: str = "home_automation_session"
     auth_session_ttl_hours: int = 12
     auth_cookie_secure_override: bool | None = True
+    auth_login_throttle_enabled: bool = True
+    auth_trust_forwarded_for: bool = False
 
     model_config = SettingsConfigDict(
         env_file=".env",