Worker di visione per stazione: modello, API, migrazione 019, execute_task (#45)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NABedeMX43pyXZbDNUgA5B

src/backend/services/station_service.py

@@ -31,6 +31,7 @@ async def create_station(
         location=data.location,
         notes=data.notes,
         active=data.active,
+        vision_worker_url=data.vision_worker_url,  # #45
         created_by=creator.id,
     )
     db.add(station)