A pull's looks open with one line counting the pages shown beside main and those main has no picture of #9768

Replaces #9765. Builders already saw main-beside-head pairs at 1440 and 390 on real pulls #9750 and #9724, so pairing works and there is nothing left to prove. What is missing is a quick way to see from the top of a pull's looks that the pairs are there, without scrolling through every page.

Done looks like:

• [x] Above the pictures, src/web/pages/looks.ts shows one line such as 4 pages beside main · 1 new to this pull, counted from the same mainLooks and head looks the compare function in that file already uses. A page main has no picture of counts as new. When main has no pictures at all, the line says so once and the per-page data-no-main lines stay as they are.
• [x] test/pull-looks-pair.test.ts holds the counts for a fixture with paired pages and one unpaired page, and the test fails without the change.
• [ ] The pull links #9750 or #9724 as the real pull where pairs show at both 1440 and 390.
• [x] bun scripts/design-lint.ts, test/looks.test.ts and test/pull-looks-pair.test.ts pass. If the line needs a new class, it goes in the looks area doc under docs/design/areas/, not in docs/DESIGN.md.

Files: src/web/pages/looks.ts, test/pull-looks-pair.test.ts. Risks: count from data the page already loads. Add no new reads of main's pictures, and build no path from user text. The line is plain text, so there is no layout shift.

Reviewed pull #9773 at its head: ticked Above the pictures, src/web/pages/looks.ts shows one line such as 4 pages beside main · 1 new to this pull, counted from the same mainLooks and head looks the compare function in that file already uses. A page main has no picture of counts as new. When main has no pictures at all, the line says so once and the per-page data-no-main lines stay as they are.; test/pull-looks-pair.test.ts holds the counts for a fixture with paired pages and one unpaired page, and the test fails without the change.; bun scripts/design-lint.ts, test/looks.test.ts and test/pull-looks-pair.test.ts pass. If the line needs a new class, it goes in the looks area doc under docs/design/areas/, not in docs/DESIGN.md.. left open: The pull links #9750 or #9724 as the real pull where pairs show at both 1440 and 390. — No one has opened either pull to confirm pairs at both widths; the description only says to check after merge..

Left open after pull #9773 landed: 1 unticked item remains (The pull links #9750 or #9724 as the real pull where pairs show at both 1440 and 390.). The planner files each as its own issue and closes this one; a person may close it, tick what is done, or say what is left. Until then the crew does not pick it again.

Closing: the one open box asked the pull description to link #9750 or #9724, the real pulls where pairs show at 1440 and 390. Both landed on main (50f445d4d, 03f0a53d7), and the summary line shipped in #9773 (abc5ef181). A builder cannot add a link to a merged pull description, so no new issue is opened for it.