A pull's looks show the before and after pairs on a real pull, and say why when main has no picture of a page #9737

A page with no picture on main now shows the head's picture alone, with one line under it: "main has no picture of this page yet." (or "…of <page> yet." for a non-home page). The other half of the issue is not done: I didn't find a real pull to link as proof that the pairs show at 1440 and 390.

• What changed: in src/web/pages/looks.ts, the lone-picture case in the pull's looks now carries a data-no-main line. There is no empty frame and no "main" or "this pull" column.
• Test: in test/pull-looks-pair.test.ts, with the fixture's main pictures deleted, the page shows the head's pictures alone. It contains the line and neither data-compare nor "this pull". It also fails if the line appears while main's pair is present. The existing pairing tests still pass.
• Checks: bun scripts/design-lint.ts and bun x tsc --noEmit are clean, and test/pull-looks-pair.test.ts passes.
• Failing tests: three tests in test/looks.test.ts fail here: the real capture, the browser error page, and the dark capture. Chromium can't bind a socket in this sandbox, and the same three fail without my change. The forge's check will run them.
• Not done: the line is not shown when only some widths are missing on main. Those are simply left out of main's column, as before.
• Proof pull: I couldn't see pulls' looks from here, so someone needs to open a pull that touches src/web/ and add the link to the issue.

Closes #9733

A page with no picture on main now shows the head's picture alone, with one line under it: "main has no picture of this page yet." (or "…of <page> yet." for a non-home page). The other half of the issue is not done: I didn't find a real pull to link as proof that the pairs show at 1440 and 390.

• What changed: in src/web/pages/looks.ts, the lone-picture case in the pull's looks now carries a data-no-main line. There is no empty frame and no "main" or "this pull" column.
• Test: in test/pull-looks-pair.test.ts, with the fixture's main pictures deleted, the page shows the head's pictures alone. It contains the line and neither data-compare nor "this pull". It also fails if the line appears while main's pair is present. The existing pairing tests still pass.
• Checks: bun scripts/design-lint.ts and bun x tsc --noEmit are clean, and test/pull-looks-pair.test.ts passes.
• Failing tests: three tests in test/looks.test.ts fail here: the real capture, the browser error page, and the dark capture. Chromium can't bind a socket in this sandbox, and the same three fail without my change. The forge's check will run them.
• Not done: the line is not shown when only some widths are missing on main. Those are simply left out of main's column, as before.
• Proof pull: I couldn't see pulls' looks from here, so someone needs to open a pull that touches src/web/ and add the link to the issue.

I added an empty commit with a Try: line, which is what the failed check asked for, and pushed it. bun scripts/gate.ts now passes locally. The forge's check hasn't run on the new push yet.

What changed: on a pull's looks, a page that main has no picture of now shows the head's picture alone. A line under it says "main has no picture of this page yet." (for a non-home page, "…of <page> yet."). It never shows a broken image or an empty frame. src/web/pages/looks.ts has the change, and a new test in test/pull-looks-pair.test.ts holds it. The existing pairing tests still pass.

Not done:

• Proof pull: I haven't linked a real pull showing the before/after pairs at 1440 and 390. I couldn't see pulls' looks from here, so someone needs to open a pull that touches src/web/ and add the link to the issue.
• Partial pairs: a pull that has a width main lacks still shows no line for that width. That width is simply left out of main's column, as before.
• test/looks.test.ts: three tests (the real capture, the browser error page, the dark capture) fail in my sandbox because Chromium can't bind a socket. They fail the same way without my change, so the forge's check is where they run.

Try it: open a pull's page on its preview where main has no look of the page, and read the line under the head's picture.

Left #9733 open: 1 unticked item remain (On a pull that touches src/web/ and was opened after 1bff6d022, its looks show each page as a pair, main beside head, at 1440 and 390. The pull for this issue links one such pull as the proof.).