feat(sync): add opds_catalog replica kind (plaintext fields) (#4087)

Wires OPDS catalogs through replica sync as a metadata-only kind.
Plaintext fields only in this PR — encrypted credentials (username,
password) ship in the follow-up alongside the SyncPassphrasePanel UI
and Tauri keychain backend.

- Migration 009 extends the kind allowlist with 'opds_catalog'.
- replicaSchemas adds opdsCatalogFieldsSchema (name, url, description,
  icon, customHeaders, autoDownload, disabled, addedAt) with a 50-row
  per-user cap.
- New opdsCatalogAdapter is metadata-only (no `binary` capability).
  Stable cross-device id from md5("opds:" + url.lower()) so two
  devices that import the same URL converge to one row instead of
  duplicating.
- New customOPDSStore (zustand) hydrates from SystemSettings,
  publishes upserts/deletes through the replica pipeline, preserves
  local-only username/password when overlaying remote updates, and
  strips tombstones at the persistence boundary so existing
  useSettingsStore readers (useOPDSSubscriptions, pseStream,
  app/opds/page.tsx) need no migration.
- replicaPullAndApply branches on adapter.binary so metadata-only
  kinds skip the bundleDir requirement and the manifest/binary path.
- CatalogManager rewires Add / Edit / Remove / Toggle / Add-popular
  through the new store.

Plan update bundled in: tenet 8 (scalar settings sync via a bundled
row; collections sync per-record), per-kind allowlist now includes a
`settings` singleton that will collapse PRs 5 + 6+ into one bundled
adapter, and PR 4 is split into 4a (already merged) / 4b (this) / 4c
(encrypted credentials + UX).

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker/volumes/db/migrations/009_replica_opds_catalog.sql

@@ -0,0 +1,11 @@
+-- Migration 009: Extend the replicas.kind allowlist with 'opds_catalog'.
+-- The DB CHECK is belt-and-suspenders; src/libs/replicaSchemas.ts
+-- (KIND_ALLOWLIST) is the actual gate that decides which kinds the
+-- server accepts on push.
+
+ALTER TABLE public.replicas
+  DROP CONSTRAINT IF EXISTS replicas_kind_allowlist;
+
+ALTER TABLE public.replicas
+  ADD CONSTRAINT replicas_kind_allowlist
+  CHECK (kind IN ('dictionary', 'font', 'texture', 'opds_catalog'));