marker: fine-grained filter ops, clean pcap on remove

Deleting or updating a marker no longer triggers a full NIO reapply
(reset_packet_filters + re-add), which closed/reopened every sibling
marker's pcap via uBridge. Instead operate on single filters:

- stop_marker: bridge delete_packet_filter + unlink the pcap (works with
  the node stopped; filter removal is skipped, the file is still deleted).
- update_marker: bpf/tag/direction → rebuild just that filter (delete + add);
  enabled → instant toggle; color/highlight_duration → stored only.
- compute delete_marker_capture / rebuild_marker_filter + per-node routes
  (DELETE /markers/{name}, PUT /markers/{name}/rebuild) + MarkerRebuild schema.

IOU overrides _ubridge_delete_marker_filter for iol_bridge; rebuild reuses
the already-overridden add/delete/set, so IOU needs no rebuild override.

gns3server/schemas/compute/nios.py

@@ -75,3 +75,19 @@ class MarkerToggle(BaseModel):
     """
 
     enabled: bool
+
+
+class MarkerRebuild(BaseModel):
+    """
+    Body for the per-marker rebuild endpoint: re-install a single uBridge marker
+    filter with new BPF/tag/direction via ``delete_packet_filter`` + add (NOT a
+    bridge-wide reset), so sibling markers keep their pcaps open. The marker's
+    own pcap is reopened by uBridge on re-add (new capture session for the new
+    BPF), which is expected.
+    """
+
+    bpf: str
+    tag: Optional[int] = None
+    direction: Optional[str] = None
+    enabled: bool = True
+    link_id: str = ""