A forge preview's check reports the held page's owner looks, desktop and phone, with how many screens tall each is #9508

Replaces #9488. Adding /preview-admin/sample/held to forge.json app.looks would make 25 visitor looks, one over LOOKS_MAX (24) in src/apps/manifest.ts, and that is why both pulls went red. The held page does not need to be in forge.json: PREVIEW_OWNER_LOOKS in src/spawn/preview-looks.ts already takes it as the owner in every forge preview. What #9240 asked for is proof that a check measures it.

Done looks like:

• [x] forge.json and LOOKS_MAX are unchanged.
• [x] A test next to test/check-looks-api.test.ts records a forge preview check whose owner looks include /preview-admin/sample/held at desktop and phone. It asserts that the commit's check in the API lists both, each with its screens-tall figure. The test fails if the held page is removed from PREVIEW_OWNER_LOOKS.
• [x] docs/features/vitals-screens.md says in one line that the held page is measured as an owner look, not a visitor look, because the visitor cap is spent.

Files: a test, docs/features/vitals-screens.md, and src/actions/runs.ts or src/http/api.ts only if the owner looks are missing from the API today. Risks: do not merge main into the branch by hand. Any commit that touches src/http/ needs a Try: line in its message, which is the gate rule that failed #9494.

Reviewed pull #9510 at its head: ticked forge.json and LOOKS_MAX are unchanged.; A test next to test/check-looks-api.test.ts records a forge preview check whose owner looks include /preview-admin/sample/held at desktop and phone. It asserts that the commit's check in the API lists both, each with its screens-tall figure. The test fails if the held page is removed from PREVIEW_OWNER_LOOKS.; docs/features/vitals-screens.md says in one line that the held page is measured as an owner look, not a visitor look, because the visitor cap is spent..