One test walks every public page and fails any that lacks a title, description, og tags or canonical URL #9637

I added test/public-head.test.ts, and every page it walks already passes, so pageHead and the pages needed no changes. The new test, bun x tsc --noEmit and scripts/gate.ts are clean. I ran only the new test file, not the whole suite.

What the test does

• It seeds a public repo with an issue and a pull, plus a public app and a catalog pack, and boots the forge.
• It fetches these as a stranger: /, /explore, /alice/shown (repo), /alice/widget (app), /alice/shown/issues/1, /alice/shown/pulls/2, /packs, /packs/<pack>, /api, /agents and /changelog.
• It fails with path: tag for a missing or empty <title>, meta name=description, og:title, og:description, og:image or link rel=canonical. It also fails when the canonical is not an absolute URL on this forge, and when a page doesn't answer 200.
• A second test checks that the checker itself reports a blank title, a missing og:image and a canonical on another host.

Routes I changed from the issue's list or left out

• The router has no /docs route. I used /api and /agents as the docs pages a stranger can open.
• Left out, with the reason in a comment in the test: pages that redirect a stranger to sign in (/map, /new, /board, /feed) and the non-HTML routes (/changelog.atom, /sitemap.xml). test/og-tags.test.ts already covers the sign-in and sign-up forms.

Not done

• I did not add twitter:card or card-image checks, because test/og-tags.test.ts already covers them.

Closes #9625

I added test/public-head.test.ts, and every page it walks already passes, so pageHead and the pages needed no changes. The new test, bun x tsc --noEmit and scripts/gate.ts are clean. I ran only the new test file, not the whole suite.

What the test does

• It seeds a public repo with an issue and a pull, plus a public app and a catalog pack, and boots the forge.
• It fetches these as a stranger: /, /explore, /alice/shown (repo), /alice/widget (app), /alice/shown/issues/1, /alice/shown/pulls/2, /packs, /packs/<pack>, /api, /agents and /changelog.
• It fails with path: tag for a missing or empty <title>, meta name=description, og:title, og:description, og:image or link rel=canonical. It also fails when the canonical is not an absolute URL on this forge, and when a page doesn't answer 200.
• A second test checks that the checker itself reports a blank title, a missing og:image and a canonical on another host.

Routes I changed from the issue's list or left out

• The router has no /docs route. I used /api and /agents as the docs pages a stranger can open.
• Left out, with the reason in a comment in the test: pages that redirect a stranger to sign in (/map, /new, /board, /feed) and the non-HTML routes (/changelog.atom, /sitemap.xml). test/og-tags.test.ts already covers the sign-in and sign-up forms.

Not done

• I did not add twitter:card or card-image checks, because test/og-tags.test.ts already covers them.