fix: Remove mock data fallback in production for better error visibility

- Removed mock data fallback from /signals endpoint
- Now returns HTTP 503 with clear error messages when protocol servers are unavailable
- Protocol servers are disabled in production, so dashboard will show clear error messages
- This ensures we can properly test connectivity issues and don't mask real problems

src/dashboard/api.py

@@ -622,7 +622,7 @@ async def get_signals():
         
         # Check if protocol servers are enabled before trying to connect
         if settings.opcua_enabled or settings.modbus_enabled:
-            # Try to get data from protocol servers, fallback to mock data if servers are not available
+            # Try to get data from protocol servers
             try:
                 # Initialize protocol data collector
                 from src.dashboard.protocol_clients import ProtocolDataCollector
@@ -642,18 +642,26 @@ async def get_signals():
                 # Clean up connections
                 await collector.cleanup()
                 
-                # If no signals were retrieved from protocol servers, use mock data
+                # If no signals were retrieved from protocol servers, return error
                 if not signals:
-                    logger.warning("no_signals_from_protocol_servers", fallback="using_mock_data")
-                    signals = await _generate_mock_signals(stations, pumps_by_station)
+                    logger.error("no_signals_from_protocol_servers")
+                    raise HTTPException(
+                        status_code=503,
+                        detail="No signals available from protocol servers. Please check server connectivity."
+                    )
             except Exception as e:
-                logger.error("failed_to_get_protocol_data", error=str(e), fallback="using_mock_data")
-                # Fallback to mock data
-                signals = await _generate_mock_signals(stations, pumps_by_station)
+                logger.error("failed_to_get_protocol_data", error=str(e))
+                raise HTTPException(
+                    status_code=503,
+                    detail=f"Unable to connect to protocol servers: {str(e)}"
+                )
         else:
-            # Protocol servers are disabled, use mock data
-            logger.info("protocol_servers_disabled", fallback="using_mock_data")
-            signals = await _generate_mock_signals(stations, pumps_by_station)
+            # Protocol servers are disabled, return clear error
+            logger.error("protocol_servers_disabled_in_production")
+            raise HTTPException(
+                status_code=503,
+                detail="Protocol servers are disabled in production environment. No real-time data available."
+            )
         
         # Add system status signals
         signals.extend([