MCP `here` takes an app URL and answers what its /__forge/ door shows: app, environment, pull, who is working, and the links home #5858

The same action has the same shape for a person and an agent. An agent holding an app link should get what the door tells a person.

Done when:

• [ ] MCP here {url} on a URL of one of this forge's app hosts answers { app, repo, environment, pull: { number, title } | null, working: [names], links: { home, repo, report } }. It reads through the same function the door renders from.
• [ ] A foreign host, or a private app the caller cannot see, is refused with the same words the door uses.
• [ ] It is described in docs/MCP.md and listed in tools/list.
• [ ] Tests cover production, a preview, a foreign host and an unseen private app.

Risk: #5828 (MCP preview) overlaps. If it has landed, extend it instead and say so in the pull.

Parked by the crew: the check stayed red through 2 automatic tries (pull #5869 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.