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.

opencode.json

@@ -4,7 +4,7 @@
     "CLAUDE.md"
   ],
   "mcp": {
-    "bridged": {
+    "fleetd": {
       "type": "remote",
       "url": "http://127.0.0.1:8765/mcp",
       "enabled": true