feat: enrich bare imports + remember the unresolvable

[vidaks]

Problem

Bare watch-imports land with no Hardcover id and grimmory never auto-enriches them, so an external every-30-min sweep re-submitted a REPLACE_MISSING refresh for every un-seeded book. Books that can never match (no/odd ISBN, self-pub/KDP editions Hardcover lacks) stayed un-seeded forever, so the sweep re-poked the same handful indefinitely — tens of metadata refreshes a day on days with zero new books, and no way for the operator to learn which books were hopeless.

Change

Move enrichment into colophon and give it memory.

• colophon/enrich.py + colophon enrich — read the un-seeded set, submit a REPLACE_MISSING refresh, precondition-gated like every other write (the prior bash loop wrote blind). Dry-run unless --apply.
• store.enrich_state — each sweep records observations; a book that never seeds is marked stuck after COLOPHON_ENRICH_STUCK_AFTER failed sweeps (default 6 ≈ 3h at the 30-min cadence), dropped from the sweep (the churn stops), and surfaced once in the maintain digest. Seeded/deleted books are pruned.
• digest — the daily summary lists each stuck book with a UI deep-link (COLOPHON_BOOKSTORE_URL, route /book/<id>, Authelia-gated). No destructive link in email — deletion is the operator's click-through to the UI button. maintain marks a book reported only after a successful email on an --apply run; silence thereafter = keep.

Safety

• Precondition gate (moveFilesToLibraryPattern=false + saveToOriginalFile=false) now guards the enrich refresh.
• The LLM is not involved; no new external calls beyond the existing grimmory refresh.

Test plan

• tests/test_enrich.py (14 cases): counting, stuck threshold, pruning, report-once, dry-run/apply refresh, precondition-abort, URL build, digest render. Stdlib unittest, network-free.
• Full suite: 56 tests pass; compileall clean.
• Smoked the dry-run against the live library: drove the real 6-book un-seeded set to stuck at the threshold and confirmed the sweep then submits nothing.

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