fix: replace bare except clause with Exception in WebSocket heartbeat

A bare `except:` catches everything including SystemExit and
KeyboardInterrupt, making it impossible to gracefully shut down the
server. Changed to `except Exception:` to match the intent while
allowing system signals to propagate.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

server/app/domains/trigger/api/trigger_execution_controller.py

@@ -336,7 +336,7 @@ async def subscribe_executions(websocket: WebSocket):
                         "type": "heartbeat",
                         "timestamp": datetime.now(timezone.utc).isoformat()
                     })
-                except:
+                except Exception:
                     break
         
         # Run both tasks concurrently