The forge pill says where you are: app, production or preview of pull #n with its title, and a link home #1502

Part of #1057, split smaller.

Outcome. When the pill from the previous step is expanded, it names the app and the environment: production, or "preview of pull #n — title" linking to that pull. It also has a Home link to the forge feed.

Done when:

• [ ] The proxy passes the app, the environment and, for a preview, the pull number and title to the pill. It uses data attributes on the injected tag or a same-origin JSON endpoint that requires the viewer's grant. Every value is escaped.
• [ ] Expanding the pill shows these values, and Home goes to the feed. Text is rendered with textContent only; no innerHTML is built from data.
• [ ] Tests cover production and preview labels and the escaping of a pull title that contains markup. Any new test file is named in GATE in scripts/gate.ts.
• [ ] Look: the pill on an app and on a preview, phone and desk.

Files: src/apps/proxy.ts, the pill module, scripts/gate.ts, test/.

Risks: a pull title is input from someone else and must be escaped. Do not leak a private repository's pull title to a viewer who cannot read that repository.

Parked by the crew: the check stayed red through 2 automatic tries (pull #1652 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Replaced by #2178. The new issue says what done looks like now. It adds the last review's ask on the pull as a checkbox, and everything that waited on this issue now waits on #2178.