Fix Uptime Kuma login not prompting for TOTP

The login method was returning success even when no token was received,
which happens when 2FA is required. Now properly detects tokenRequired
response and validates token before claiming success.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/kuma_client.py

@@ -128,15 +128,27 @@ class UptimeKumaClient:
             else:
                 result = api.login(username, password)
 
+            # Check if 2FA is required
+            if result.get("tokenRequired"):
+                api.disconnect()
+                raise Exception("2FA token required. Please enter your TOTP code.")
+
             token = result.get("token")
-            if token:
+            if not token:
+                api.disconnect()
+                raise Exception("Login failed: No authentication token received")
+
             save_token(token)
             self._token = token
 
             api.disconnect()
             return {"success": True, "message": "Login successful"}
         except Exception as e:
-            raise Exception(f"Login failed: {str(e)}")
+            error_msg = str(e)
+            # Re-raise with clear message for 2FA requirement
+            if "tokenRequired" in error_msg or "2fa" in error_msg.lower():
+                raise Exception("2FA token required. Please enter your TOTP code.")
+            raise Exception(f"Login failed: {error_msg}")
 
     def is_authenticated(self) -> bool:
         """Check if we have valid authentication."""