marker: make per-filter toggle fall back to NIO rebuild when the marker isn't installed

Toggle routes silently no-opped when _marker_filter_bridges lacked the filter
name, so update_marker's enabled-only short-circuit succeeded without toggling
uBridge — the controller-layer enabled was set but the uBridge filter stayed on
and kept emitting signals. Now the toggle routes raise HTTPException 404
(FastAPI handles it directly, no ERROR log); the controller's except catches it
and falls back to self.update() (NIO rebuild, which applies the marker + off).

gns3server/api/routes/compute/docker_nodes.py

@@ -423,6 +423,11 @@ async def toggle_docker_marker(
     Toggle a marker filter on/off without an NIO rebuild (ubridge contract §3.2).
     """
 
+    if marker_name not in node._marker_filter_bridges:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Marker '{marker_name}' is not installed on this node",
+        )
     await node._ubridge_set_marker_filter_state(marker_name, toggle_data.enabled)
     return {"marker_name": marker_name, "enabled": toggle_data.enabled}