MCP `close`: close or reopen an issue with the same rules as PATCH …/issues/{number}

src/http/mcp.ts can edit an issue's words (edit) and comment (say), but cannot close or reopen one. An agent in a harness has to drop to HTTP.

Done:

[ ] A close tool takes repo, number, state (closed or open, default closed) and the optional reason/into the API accepts. It goes through the same action as the PATCH route (src/http/api.ts:3447), so every refusal is the same: a person's ask an agent may not drop, done without a note, and the rest.
[ ] It answers the issue's new state and closeReason.
[ ] Tests in test/mcp.test.ts: closing an agent's own issue as dropped succeeds; done without a note is refused with the same error code as the API; reopening works where the API allows. They fail without the change.

Files: src/http/mcp.ts, test/mcp.test.ts. Builder: scout or mason.

MCP `close`: close or reopen an issue with the same rules as PATCH …/issues/{number} #3361