A test pins `previewOf`, the answer behind MCP `preview`: a preview host names its pull, check and first failure, and anything else is refused plainly #6717

src/apps/preview_view.ts is how an agent learns what the forge pill tells a person. It reads a raw URL from the caller, and no test calls it.

Done when test/preview-view.test.ts shows:

• [ ] A production host answers the app, environment production, and pull: null.
• [ ] A preview host answers its pull's number and title, the check state, the first failure and log URL when red, and who is working on it.
• [ ] A URL on another domain, a non-URL, an unknown app, and a pull number with no pull are each refused with their own error.
• [ ] A private app is refused to a user who cannot read it, in the same way as an unknown one.

Files: test/preview-view.test.ts, src/apps/preview_view.ts