A pull's looks show main's picture beside the head's, so before and after are on every pull with no one attaching them #9669

For: the owner judges a design change in one look, and a reviewer can tick "looks before and after" from the pull page.

Done looks like:

• [x] On the pull page's looks, each head look that main also has (same page, kind and theme) is shown as a pair labelled "main" and "this pull", at 1440 and 390, in light and dark. Where main has none, the head look stands alone as it does today.
• [x] Server-rendered, no new script, and no layout shift: each image keeps its width and height.
• [x] A test renders a pull with one paired look and one unpaired look, and asserts the two labels and the image URLs. It fails without the change.
• [ ] bun scripts/design-lint.ts passes, and the page's looks on the pull show the pairs.

Files: src/web/pages/looks.ts, src/web/pages/pull.ts, a test. Risk: the looks are only as private as the pull's own looks today. Reuse their access check, never a new route without it.

Parked by the crew: the check stayed red through 2 automatic tries (pull #9676 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Reviewed pull #9717 at its head: ticked On the pull page's looks, each head look that main also has (same page, kind and theme) is shown as a pair labelled "main" and "this pull", at 1440 and 390, in light and dark. Where main has none, the head look stands alone as it does today.; Server-rendered, no new script, and no layout shift: each image keeps its width and height.; A test renders a pull with one paired look and one unpaired look, and asserts the two labels and the image URLs. It fails without the change.. left open: bun scripts/design-lint.ts passes, and the page's looks on the pull show the pairs. — Lint is reported clean, but no pair was shown on the preview, so the second half is unconfirmed..

Left open after pull #9717 landed: 1 unticked item remains (bun scripts/design-lint.ts passes, and the page's looks on the pull show the pairs.). 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 work shipped. Before and after looks now come automatically on every pull (1bff6d022), and test/pull-looks-pair.test.ts holds the pairing, so this box needs no builder run.