Three medium correctness fixes:
1. **Pagination ORDER BY missing tiebreakers** — four admin list queries
sorted by a timestamp or `chapters.number` with no stable secondary
sort. Add `id` tiebreakers across `repo::admin_view`,
`repo::admin_audit`, `repo::bookmark`.
2. **`enqueue_pages` NOT EXISTS read-then-insert race** — concurrent
admin clicks could land duplicate analyze_page jobs. Migration 0031
adds a partial unique index mirroring 0014; query relies on
`ON CONFLICT DO NOTHING`.
3. **`record_duration` overwrote a prior done row's duration on a
non-terminal failed retry of a force-re-analyze.** Gate the call
on "did this attempt actually write a row?".
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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