MCP `app_deploy`: redeploy or stop an app's production or a preview, with the same rules as the API #4755

Intent: an agent that changed an app's environment can redeploy it, or stop a preview, without a page.

Done:

• [ ] src/http/mcp.ts has an app_deploy tool, placed right after apps, taking repo, env (production or a pull's preview) and action (redeploy | stop) and calling what POST /api/v1/repos/:owner/:name/app/:env/redeploy and …/stop call: the same permissions, the same queued answer
• [ ] docs/MCP.md has its row beside apps
• [ ] test/mcp-app-deploy.test.ts: a writer queues a redeploy and stops a preview; a reader is refused; an unknown env is refused

Risks: test/mcp-size.test.ts holds tools/list under a 37,000-byte headroom; keep the description to one short sentence, and if the headroom fails after a rebase, shorten this tool's own description, not another's. Other MCP tools are being added in parallel: put this one exactly where named so the hunks do not meet.