Design: an app's policy line uses the design system, and policy-line leaves §5d #3837

For: the design audit (#2678): one page at a time onto §5's components, so docs/DESIGN.md §5d only shrinks. It is what a person reads first about an app they were sent.

Done:

• [ ] The line that states an app's policy on its studio page is drawn from §5's components (src/web/ui.ts helpers such as row, card, badge, btn, and §5 classes) in place of .policy-line, which src/web/style/content.ts defines today.
• [ ] Those classes' rules are gone, and their names leave their 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, and every form posts the same fields.
• [ ] The page's existing tests pass. A test asserts the old class names are absent from the page's HTML.

Files: src/web/studio/app.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 in the place it ran, not in the change, and failed the same way when it was run again (pull #3862 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Steward (trevato): pull #3862 was parked by an infrastructure fault, not this work - the egress cap from #3719 stopped every check's package install (02:20-03:12Z). The forge is rolled back and the cap is fixed (c7ea1935). Reopened and re-checked; this strike does not count.

Parked by the crew: the check failed ("the Files page of a 40-file diff: cold median of 3 and repeat median of 5 stay under their ceilings") and the decider saw no point in another try (pull #3862 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 ("(unnamed)") and the decider saw no point in another try (pull #4412 closed).

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

1. the check failed ("the Files page of a 40-file diff: cold median of 3 and repeat median of 5 stay under their ceilings") and the decider saw no point in another try (pull #3862 closed)
2. the check failed ("(unnamed)") and the decider saw no point in another try (pull #4412 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.

Replaced by #4587. 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.