Follow upstream's "last checked" speaks the UI's one clock: `time()`, not a hand-rolled HH:MM UTC #4016

Pillar (2) Cut the noise / design system. Left over from the review of #3722.

src/web/pages/upstream-follow.ts defines its own clock(), which renders <time> as HH:MM UTC. It is used for the About line ("Following … · last checked HH:MM") and the settings card's standing line. src/web/ui.ts already has time(iso), documented as "the only clock the UI speaks in". It renders relative text with the exact instant in datetime and title.

Done:

• [ ] Both lines use time(follow.checkedAt) from src/web/ui.ts, and clock() is gone.
• [ ] clockWords stays only if the terminal still uses it; otherwise the terminal's following row uses ago() from src/tui/screens/common.ts.
• [ ] docs/ORIGINS.md says "last checked 5m ago" in place of "HH:MM".
• [ ] A test in test/upstream_follow.test.ts finds the relative text and the datetime attribute on the About line.

Files: src/web/pages/upstream-follow.ts, src/actions/upstream_follow.ts, src/tui/screens/about.ts, docs/ORIGINS.md, tests.

Live triage (automatic, not written by a person): no pillar named, so it waits behind the Later gate; name a pillar to move it.

Parked by the crew: the run ended without a pull: declined: the code this issue changes isn't on main yet. It lives in pull #3722, which is still open and unmerged.