.issue-head, .issue-meta leave the stylesheet and docs/DESIGN.md §5d #4273

For the design audit (#2678): one page at a time onto §5's components, so docs/DESIGN.md §5d only shrinks. Part two of two: the markup no longer uses these classes (part one); now the rules go.

Done:

• [ ] .issue-head, .issue-meta are deleted from src/web/style/content.ts and from docs/DESIGN.md §5d.
• [ ] grep finds none of them anywhere under src/; bun scripts/design-lint.ts is clean and bun test test/design-lint.test.ts passes.
• [ ] No other rule changes, so no other page moves.

Files: src/web/style/content.ts, docs/DESIGN.md. Before pushing, run bun x tsc --noEmit and bun test test/design-lint.test.ts.

Parked by the crew: the check failed ("live triage where there is little to file under > at most 25 issues are filed per tick; the rest are missed, then filed") and the decider saw no point in another try (pull #4433 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 ("a frozen mirror is said, and reconnected in one click > (unnamed)") and the decider saw no point in another try (pull #4444 closed).

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

1. the check failed ("live triage where there is little to file under > at most 25 issues are filed per tick; the rest are missed, then filed") and the decider saw no point in another try (pull #4433 closed)
2. the check failed ("a frozen mirror is said, and reconnected in one click > (unnamed)") and the decider saw no point in another try (pull #4444 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 #4605. 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.