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/controller/project.py

@@ -924,6 +924,41 @@ class Project:
                 }
         return result
 
+    async def pause_all_markers(self):
+        """
+        Pause marker signal+pcap emission on every node hosting a marker
+        (``marker pause`` per capture node's uBridge). Node-deduplicated and
+        best-effort: a node hosting markers on several links is paused once,
+        and a node that is down or running an old compute is skipped.
+        """
+
+        seen = set()
+        for link in list(self._links.values()):
+            for info in link.markers.values():
+                node_id = info.get("capture_node_id")
+                if not node_id or node_id in seen:
+                    continue
+                seen.add(node_id)
+                try:
+                    await self.get_node(node_id).post("/markers/pause")
+                except Exception:
+                    pass
+
+    async def resume_all_markers(self):
+        """Resume marker signal+pcap emission on every marker-hosting node."""
+
+        seen = set()
+        for link in list(self._links.values()):
+            for info in link.markers.values():
+                node_id = info.get("capture_node_id")
+                if not node_id or node_id in seen:
+                    continue
+                seen.add(node_id)
+                try:
+                    await self.get_node(node_id).post("/markers/resume")
+                except Exception:
+                    pass
+
     @property
     def marker_definitions(self):
         """