Design: /explore's rows and filters use §5's row and filters, and the explore-* classes leave §5d #3801

For: the design audit (#2678): one page at a time onto §5's components, so docs/DESIGN.md §5d only shrinks. /explore is where apps, forges and people are ranked.

Done:

• [ ] /explore's ranked rows and its filters is drawn from §5's components (src/web/ui.ts helpers, §5 classes) in place of .explore-filters .explore-line .explore-main .explore-name .explore-row, which src/web/style/content.ts defines today.
• [ ] Those classes' rules are gone, and their names leave the style/content.ts, page furniture bullet of docs/DESIGN.md §5d. bun scripts/design-lint.ts passes, and so does --update with a lower or equal baseline.
• [ ] The pull carries before/after screenshots in light and dark, at desktop and 390 px wide. Nothing a person reads or taps is lost.
• [ ] The page's existing tests pass. A test asserts the old class names are absent from the page's HTML.

Files: src/web/studio/explore.ts, src/web/style/content.ts, docs/DESIGN.md, the page's test. Risk: another page borrowing one of these classes. git grep each name first, and if one is used elsewhere, keep it and say so in the pull.

Parked by the crew: the check failed ("the off-box mirror > a snapshot lands in both buckets, and the page's facts say so") and the decider saw no point in another try (pull #3821 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Parked by the crew: the check failed ("migrate: after > (unnamed)") and the decider saw no point in another try (pull #4426 closed).

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the check failed ("the off-box mirror > a snapshot lands in both buckets, and the page's facts say so") and the decider saw no point in another try (pull #3821 closed)
2. the check failed ("migrate: after > (unnamed)") and the decider saw no point in another try (pull #4426 closed)

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Split into #4583 and #4584. Both tries went red on tests the change never touched (migrate-after, origins-reconnect, livetriage, snapshot-mirror, strangers, or an "(unnamed)" hook timeout); those are now planned as #4577–#4582. The fresh issue keeps the diff to the named files and says to run design-lint and lower the baseline in the same pull, and splits the markup move from the rule removal.