feat: accept link=<link_id> on the replay range and frames endpoints

Narrows the merged frame stream to one capture source BEFORE counting,
slicing and bucketing (frame_count / frames | buckets all recomputed on
the narrowed set), AND-composing with the display filter. A pure
identity filter applied before any engine work — only the selected
link's pcap gets a sharkd pass, so link+filter is cheaper than filter
alone.

Two boundaries by contract with the Web UI:
- sources[] stays the tag's stable inventory: every capture source
  listed with engine-free TOTAL counts, unaffected by link/filter — a
  source dropdown must not shrink when the view narrows (this also
  settles sources[].count on total counts rather than post-filter
  matches, which no spec ever required)
- an unknown link_id matches nothing: frame_count 0, start null, empty
  frames/buckets — the same shape as a zero-match display filter,
  deliberately not a 404; an empty link param is treated as absent

gns3server/api/routes/controller/projects.py

@@ -242,6 +242,7 @@ async def _replay_response(awaitable):
 async def replay_tag_range(
     tag: int,
     filter: Optional[str] = None,
+    link: Optional[str] = None,
     project: Project = Depends(dep_project),
 ) -> dict:
     """
@@ -259,12 +260,20 @@ async def replay_tag_range(
     counting and slicing — start / end / frame_count / frames | buckets are
     all computed on the matching frames only. An invalid expression is a 400
     carrying sharkd's original error text (for inline display in the UI
-    filter bar). Requires sharkd — 501 without it.
+    filter bar).
+
+    ``link`` narrows the frame stream to one capture source (link_id),
+    AND-composing with ``filter``; ``sources`` always lists the tag's full
+    inventory regardless. An unknown link_id yields an empty timeline (same
+    shape as a zero-match filter), not a 404. Requires sharkd — 501 without
+    it.
 
     Required privilege: Project.Audit
     """
 
-    return await _replay_response(marker_replay.build_timeline(project, tag, filter_expr=filter))
+    return await _replay_response(
+        marker_replay.build_timeline(project, tag, filter_expr=filter, link_id=link)
+    )
 
 
 @router.get(
@@ -277,6 +286,7 @@ async def replay_tag_frames(
     window_ms: int = 100,
     limit: int = 1000,
     filter: Optional[str] = None,
+    link: Optional[str] = None,
     project: Project = Depends(dep_project),
 ) -> dict:
     """
@@ -285,15 +295,19 @@ async def replay_tag_frames(
     ``{"frames": []}``. The tag gate applies (409 while any marker captures).
 
     ``ts`` must be the exact string returned by the range response — never
-    re-serialize it through a float. ``filter`` (optional display filter) has
-    the same semantics as on the range endpoint. Requires sharkd — 501
-    without it.
+    re-serialize it through a float. ``filter`` and ``link`` (optional
+    display filter / capture-source link_id) have the same semantics as on
+    the range endpoint — windows and the histogram always agree. Requires
+    sharkd — 501 without it.
 
     Required privilege: Project.Audit
     """
 
     return await _replay_response(
-        marker_replay.query_frames(project, tag, ts, window_ms=window_ms, limit=limit, filter_expr=filter)
+        marker_replay.query_frames(
+            project, tag, ts, window_ms=window_ms, limit=limit,
+            filter_expr=filter, link_id=link,
+        )
     )