feat: add tag-keyed aggregate replay over paused markers' pcaps

Markers on different links sharing a tag form one distributed capture
session. Once every marker under the tag is paused (409 otherwise), three
read-only endpoints replay it:

- GET .../markers/tags/{tag}/replay/range merges the per-marker pcaps by
  scanning 16-byte record headers only (no tshark) into a timestamp-
  ordered frame list (per-second buckets above a 5000-frame cap)
- GET .../replay/frames?ts=&window_ms= returns frames in [T, T+window];
  an empty window is a normal empty array
- GET .../replay/frame/detail lazily decodes one frame the user opened:
  raw bytes for the hex view read straight from the pcap, protocol tree
  from 'tshark -T pdml' mapped isomorphically to JSON (every attribute
  survives, values stay strings). tshark reads a /tmp scratch copy with a
  scratch HOME — hardened profiles deny it the project directory.

Sort key is (ts, source file, frame number): ts is not unique across a
merge. The ts parameter round-trips as the exact string from the frame
list. Round-trip tests pin the PDML→JSON fidelity (element count and
attribute coverage).

gns3server/controller/project.py

@@ -519,6 +519,17 @@ class Project:
         os.makedirs(path, exist_ok=True)
         return path
 
+    @property
+    def markers_directory(self):
+        """
+        Location of the marker pcap files (same layout the compute side writes
+        via ``markers_working_directory`` — single-server deployments share the
+        project directory, which is what tag replay reads).
+        """
+        path = os.path.join(self._path, "project-files", "markers")
+        os.makedirs(path, exist_ok=True)
+        return path
+
     @property
     def pictures_directory(self):
         """