Phase 6: sync jobs, inquiry and order forms

- Sync scheduler in the content service with a per-job cache (sync_cache),
  sync_runs reporting and Healthchecks pings. Jobs: Archidekt, BoardGameGeek,
  cover art (Open Library, TMDB, AniList), Suwayomi and Kavita reading
  progress, Bambuddy filament and Homebox material stock. A note's own value
  always wins over a synced one.
- PersonalReader: updates only Library notes with a matching anilistId,
  changes to Greg's notes are held for review; Reading series with no note
  show as suggestions on the admin Overview.
- /api/inquiries and /api/orders: Turnstile, rate limits, a saved copy in the
  content service (intake token) plus email over SMTP. Orders are re-checked
  against the live notes: accepted only when the category's ordersOpen is
  true and the line has capacity.
- Admin Inbox for saved submissions. Options' inStock is optional so synced
  stock can fill it. All settings from process.env; .env.example per service.
- Sources could not be reached from the build environment; parsers are tested
  against fixtures labelled as not live.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012aSbo2D1qP8cMFQCykf7kx

services/content/test/sync/fixtures/kavita-series.sample.json

@@ -0,0 +1,5 @@
+[
+  { "id": 11, "name": "Sample Light Novel", "localizedName": "", "pages": 400, "pagesRead": 400, "latestReadDate": "2026-10-02T21:15:00", "libraryId": 2 },
+  { "id": 12, "name": "Sample Ongoing Novel", "localizedName": "Sample Ongoing Novel (EN)", "pages": 300, "pagesRead": 120, "latestReadDate": "2026-10-09T08:00:00", "libraryId": 2 },
+  { "id": 13, "name": "Sample Unread Novel", "pages": 250, "pagesRead": 0, "latestReadDate": "0001-01-01T00:00:00", "libraryId": 2 }
+]