CB-622 lead follow-up: the three changes no worker could make

1. opencode.json — mount key bridged -> fleetd. Unit C could not do this:
   the file is neutralized by the worktree overlay, so every worker sees a
   stub and correctly reported it held no mount key. Tracked as CB-628.

2. e2e/bridge_ask_transcript.md keeps its name. It is a dated record of a
   run on 2026-07-16 that really did call bridge_ask, and its first line
   says so. The harness now writes fleet_ask_transcript.md for new runs;
   its header already says 'Live fleet_ask', so the two now agree.

3. docs/MCP-Contract.md line 20 — the historical banner describes section
   6, and section 6 now says fleet_ask.

e2e/bridge_ask_test.py

@@ -210,7 +210,7 @@ def grade(rec):
 
 
 def write_transcript(out_dir, rec, meta):
-    path = out_dir / "bridge_ask_transcript.md"
+    path = out_dir / "fleet_ask_transcript.md"
     g, note = grade(rec)
     with path.open("w") as f:
         f.write(f"# Live fleet_ask — reverse rendezvous — {datetime.now():%Y-%m-%d %H:%M}\n\n")