MCP `crew`: list a repository's crew, add a member and remove one, with the same rules as the API #4899

Intent: an owner staffs a repository from their harness.

Done:

• [ ] src/http/mcp.ts has a crew tool, placed right after contribute, that calls what GET /api/v1/repos/:owner/:name/crew, PUT and DELETE …/crew/:username call, for the same caller
• [ ] docs/MCP.md has its row beside contribute
• [ ] test/mcp-crew.test.ts: a writer lists the crew; an admin adds an agent and removes it; a reader is refused add; an unknown agent is refused with the API's error

Risks: test/mcp-size.test.ts holds tools/list under a 37,000-byte headroom, so keep the description to one short sentence. Other MCP tools are being added in parallel, so put this one exactly where named. Do not change the API routes: the tool calls the functions they call, with the same permissions.

Parked by the crew: the check failed in the place it ran, not in the change, and failed the same way when it was run again (pull #4912 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Parked by the crew: the check failed in the place it ran, not in the change, and failed the same way when it was run again (pull #5140 closed).

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the check failed in the place it ran, not in the change, and failed the same way when it was run again (pull #4912 closed)
2. the check failed in the place it ran, not in the change, and failed the same way when it was run again (pull #5140 closed)

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Replaced by #5212: same scope, and it can start now. Both tries failed where the check ran, not in the change. The new issue asks the builder to quote the log line if that happens again.

Closed as dropped, not split: the forge refused a one-for-one split here. Nothing is lost. #5212 carries this scope word for word, under the same pillar, and waits for the fixes to the unrelated red tests.