Fix healthcheck + external URL in silent auth middleware

- Add /health endpoint, update healthcheck to use it
- Use configured base URL instead of internal Docker URL
- Add /health to skip prefixes for silent auth

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/routers/home.py

@@ -16,6 +16,12 @@ from ..dependencies import get_templates, get_current_user
 router = APIRouter()
 
 
+@router.get("/health")
+async def health():
+    """Health check endpoint — always returns 200."""
+    return {"status": "ok"}
+
+
 async def get_user_stats(actor_id: str) -> dict:
     """Get stats for a user."""
     import database