feat: times in the reader's own zone; the audit log shows exact moments (milestone 490)

- users.time_zone (0034). An account without one takes the browser's zone
  on its first page (POST /account/time-zone/adopt, never over a choice made
  by hand); the session follows the account on every request.
- /account: who you are and the zone every page writes its times in,
  reached from your name in the sidebar.
- formatting.when: 'Today 06:58', 'Yesterday 23:41', 'Tue 6 Oct 14:12',
  '6 Oct 2025 14:12', 24-hour, in the reader's zone; |ago's hover is the
  exact local moment instead of UTC; tz_label() for column headers.
- Audit log: When (EDT) with exact times, one detail fact a line, on classes.
- tzdata in the image, and the airgapped smoke checks a zone resolves.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.forgejo/workflows/ci.yml

@@ -206,6 +206,10 @@ jobs:
           # tini is PID 1, so zombies are reaped and SIGTERM reaches Steward.
           test "$(docker exec "$SMOKE-app" cat /proc/1/comm)" = "tini"
 
+          # The zone database is in the image, so a reader's zone resolves
+          # instead of quietly falling back to UTC (milestone 490).
+          docker exec "$SMOKE-app" python -c 'from zoneinfo import ZoneInfo; ZoneInfo("America/New_York")'
+
           # A fresh database lands on first-run setup: a real page, its assets
           # served by Steward itself, and no third-party host in it (rule 155).
           fetch / > /tmp/smoke-page.html