feat(mcp): codeman mcp, a Model Context Protocol server for any MCP client

Agents pick tools from MCP clients and registries, and Codeman had no MCP
surface: an assistant in Claude Desktop, Cursor, Codex or Gemini CLI could
not start or drive Codeman sessions without hand-written HTTP calls.

`codeman mcp` is a stdio MCP server and a CLIENT of the existing HTTP API
(it reuses codeman agent's transport and guards; no new route). Seven
tools: list_sessions, start_session, send_prompt, wait_for_session,
read_output, interrupt_session, delete_session.

- Dual-era: answers the legacy initialize handshake (2024-11-05 to
  2025-11-25) and the 2026-07-28 revision (per-request _meta,
  server/discover, resultType, and the ttlMs/cacheScope hints a modern
  tools/list must carry: Claude Code 2.1.296 drops every tool without
  them).
- Never guesses a server: the URL comes from --url or CODEMAN_API_URL.
  Unconfigured, it still lists its tools and every call says how to
  configure it.
- Prompting, interrupting and deleting are limited to sessions the process
  started (or, inside a Codeman pane, that session's own workers) unless
  --allow-any-session; never its own session. Control bytes are refused
  before any request.
- Waits default to 45 s (Codex's MCP tool timeout is 60 s), max 600 s.
- read_output returns text only: a client that prefers structuredContent
  otherwise showed the model metadata instead of the output.
- config/mcp-registry/server.json and package.json mcpName prepare the
  official MCP registry listing; sync-plugin.mjs keeps its version.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/extending-codeman.md

@@ -167,6 +167,10 @@ agent skill instead of teaching it these calls by hand: `skills/codeman` in the
 per-case injection on Claude session create). The skill carries the guard, the
 safety rules, and verified wait/orchestration recipes.
 
+If the caller speaks the Model Context Protocol (Claude Desktop, Cursor, Codex, any MCP
+client), point it at `codeman mcp` instead: seven tools over these same endpoints,
+configured with `CODEMAN_API_URL`. See the README section "MCP server".
+
 The common ones:
 
 ```bash