marker: rework pause/resume from project-wide to per-definition

The project-wide mute (POST /markers/pause|resume + _markers_paused) paused
every marker with one button. The actual need is per-rule control: pause one
definition and toggle only its inherited global-{name} copies across all links.

- Drop project-level: _markers_paused (init/asdict/load/start_all), the
  pause_all/resume_all_markers methods, and the /markers/pause|resume routes.
- Add per-definition: a persisted `paused` flag on each definition;
  pause/resume_marker_definition fan out update_marker(enabled) to every
  global-{name} copy — instant, via the existing enable_packet_filter toggle
  (no NIO rebuild, pcap/emitted preserved). New links inherit a paused
  definition already off (inherit_marker passes enabled=not paused).
- start_marker takes an enabled kwarg; update_marker's enabled-only short-circuit
  now also covers inherited copies so def pause/resume is instant.
- Routes: POST /marker-definitions/{name}/pause|resume.
- Docs + tests updated.

gns3server/controller/link.py

@@ -131,6 +131,7 @@ class Link:
             direction=marker_def.get("direction"),
             color=marker_def.get("color"),
             highlight_duration=marker_def.get("highlight_duration"),
+            enabled=not marker_def.get("paused", False),
             inherited_from=def_name,
         )
 
@@ -341,7 +342,7 @@ class Link:
 
         raise NotImplementedError
 
-    async def start_marker(self, name, bpf, tag=None, direction=None, capture_node_id=None):
+    async def start_marker(self, name, bpf, tag=None, direction=None, capture_node_id=None, enabled=True):
         """
         Attach a traffic-insight marker to this link (base — UDPLink overrides).
         """