marker: drive uBridge enabled/pause/resume in real time

Wire gns3-server to uBridge's real-time marker controls (contract
../ubridge/doc/gns3server-integration.md §3.2), in three layers:

A. enabled reaches uBridge — _markers_for_node no longer drops disabled
   markers controller-side; it carries `enabled` in the NIO spec. apply
   installs every marker then issues `enable_packet_filter … off` for the
   disabled ones (base_node bridge / iou iol_bridge; old-ubridge errors
   downgrade to a warning so a toggle can't break link create).

B. instant per-filter toggle — apply records name→bridge so a new
   `_ubridge_set_marker_filter_state` can flip a running filter with
   `enable_packet_filter on|off` (iou overrides for iol_bridge + bay/unit).
   Each marker-capable node type gains PUT /markers/{name}; update_marker
   short-circuits to it when only `enabled` changes (no NIO rebuild, no pcap
   flush), falling back to reset+reapply if the route is unavailable.

C. global pause/resume — `_ubridge_marker_pause/resume` send `marker pause`
   / `marker resume` direct to the hypervisor (pause stops signal+pcap,
   resume instant, sink retained). Six node-type routes add POST
   /markers/pause|resume; project.pause_all/resume_all_markers fan out to
   each capture node (deduped, best-effort); REST exposes
   POST /projects/{id}/markers/pause|resume.

Toggling enabled and pause/resume are now both instant — only marker create
or a bpf change still go through reset+reapply.

gns3server/api/routes/controller/projects.py

@@ -219,6 +219,37 @@ def get_project_markers(project: Project = Depends(dep_project)) -> dict:
     return project.markers
 
 
+@router.post(
+    "/{project_id}/markers/pause",
+    status_code=status.HTTP_204_NO_CONTENT,
+    dependencies=[Depends(has_privilege("Project.Modify"))]
+)
+async def pause_project_markers(project: Project = Depends(dep_project)) -> None:
+    """
+    Pause marker signal+pcap emission project-wide (``marker pause`` on every
+    marker-hosting node's uBridge; resume is instant, sink retained).
+
+    Required privilege: Project.Modify
+    """
+
+    await project.pause_all_markers()
+
+
+@router.post(
+    "/{project_id}/markers/resume",
+    status_code=status.HTTP_204_NO_CONTENT,
+    dependencies=[Depends(has_privilege("Project.Modify"))]
+)
+async def resume_project_markers(project: Project = Depends(dep_project)) -> None:
+    """
+    Resume marker signal+pcap emission project-wide.
+
+    Required privilege: Project.Modify
+    """
+
+    await project.resume_all_markers()
+
+
 # ---------------------------------------------------------------------------
 # Project-level marker definitions (global rules inherited by every link)
 # ---------------------------------------------------------------------------