Signed out, the toolbar page of a public app offers "Report a problem, no account needed" beside Sign in #6287

The Lost test and the Muse test both ask for this: from any app you can say something. Today toolbarPage (src/web/studio/toolbar.ts) gives a signed-out visitor only "Sign in to comment". The app's own /__forge/ page and Link header already offer the anonymous report.

Done when:

• [ ] Signed out on a public repository's app, the toolbar page draws a "Report a problem" link with the words "no account needed". It goes to the repository's anonymous report form (/<owner>/<name>/report), carrying this page's address, and the form shows that address.
• [ ] A private repository's toolbar page draws no such link. A guest still sees only Sign in, and the page still answers 404 where it does today.
• [ ] A test fetches the toolbar page signed out for a public app and a private app and checks for the link and its absence. A second test follows the link and finds the address on the form.
• [ ] bun scripts/design-lint.ts passes. The link uses the existing btn part.

Files: src/web/studio/toolbar.ts, the report page if it does not yet read a page parameter, a test. Risk: the page address is visitor-supplied. Keep it passing through pageAddress and escape it.