Every post's time on the home timeline shows its exact UTC on hover #6063

Part of #5821, split out. The owner catching up can read exactly when something happened.

Done when:

• [ ] feedCard and thoughtCard in src/web/studio/feed.ts render their time with time() from src/web/ui.ts (a <time datetime> whose title is YYYY-MM-DD HH:MM UTC), not bare timeAgo.
• [ ] The live fragment (liveFeedFragment) renders the same markup.
• [ ] A test renders one feed card and one thought card and finds <time datetime="…" title="… UTC"> in each; it fails on main.
• [ ] bun scripts/design-lint.ts passes.

Files: src/web/studio/feed.ts, a test under test/. Risk: the feed's cached HTML (home_cache.ts) must not freeze a relative time longer than it does today.

Parked by the steward, 2026-10-26 (owner: "get us unclogged now then resume everything else"). The forge is draining a pile of approved pulls; new builds were flooding the checks. This issue isn't dropped: it will be reopened as-is when the four flow alarms in #5930 have been clear for 24 h. The list is kept in the steward's parked-2026-10-26 file.