feat(facets): facet registry, Batch A server params, genre model v2, facets endpoint

Phase 1 + backend of Phase 2 of the faceted-navigation plan. One
declarative facet registry (services/facet_registry.go) drives the
bookshelf filter system; a drift-guard unit test reflects over the
generated SearchMediaItemsUnifiedParams so a registry entry and its
sqlc.narg block can never disagree silently.

- Nine new filter params on SearchMediaItemsUnified: story_arc,
  imprint, edition (scalar-fuzzy), age_rating, format_group,
  manga_type, reading_direction (exact), explicit, abridged
  (presence-bound bools). Comma = OR-within multi-select on every
  text facet; AND-across-facets unchanged.
- Genre model v2 (user rule: a subgenre is not a genre, it's a tag):
  genre_lexicon.go rebuilt as shelf set + subgenre->shelf map;
  pickSmartGenre picks direct shelf > mapped subgenre > Fiction floor
  > empty (unknown-only stays tags-only). Type-words (Manga, Comics,
  Graphic Novel) join the demote list. Both 'adventure' and 'action &
  adventure' are shelves — provider data uses both and the verified
  traces pin them.
- Language filter UX: comma elements normalize through the ingest
  language map, so display names ('English') match rows stored as ISO
  codes ('en'). The language autocomplete now serves display names.
- NEW GET /api/media-items/facets?facet=X&library_id=... — registry-
  driven value+count listing (14 static per-column queries, family-lens
  join); language values carry display names; bool/range facets 400.
- Family-lens gates: an explicit hidden-library library_id is now a
  403 on the search endpoints (was a silent empty set) — JSON branch
  and HTMX grid partial both.
- handlers.ParseMediaSearchParams is the SINGLE param parser for the
  search JSON endpoint and the HTMX grid partial; the HTML branch
  previously dropped publisher_filter and narrator_filter silently.

Pins: docs/contract_pins.md changelog entries (additive request
params; new facets endpoint). Tests: facet_registry_test.go (shape +
SQL drift guard + library-type union), series_parsing_test.go genre-v2
cases, facets_integration_test.go (param filtering e2e, counts,
language display, 403s) — container runner.

docs/contract_pins.md

@@ -161,3 +161,22 @@ cover_image_path, has_conflict, format_group, badge`.
 - `author_filter` / `publisher_filter` are now per-element against the
   arrays; a comma-joined value is OR-within-facet multi-select. The
   param NAMES and single-value behavior are unchanged.
+
+## 2026-10-19 — Faceted navigation Batch A: new filter facets
+
+- `GET /api/media-items/search` accepts ADDITIVE REQUEST params (query
+  string, response shapes unchanged): `story_arc_filter`,
+  `imprint_filter`, `edition_filter` (scalar-fuzzy),
+  `age_rating_filter`, `format_group_filter`, `manga_type_filter`,
+  `reading_direction_filter` (exact), `explicit_filter`,
+  `abridged_filter` (bool: absent = unset, "true"/"false" = bound).
+  A comma-joined value is OR-within-facet multi-select on every new
+  TEXT facet (the SQL splits via string_to_array). `services/facet_registry.go`
+  is the Go-side source of truth; the drift-guard unit test
+  (`TestFacetRegistrySQLDrift`) pins registry ↔ SQL agreement.
+- Genre model v2 changes SCANNER OUTPUT (not a wire contract): sidecar
+  genre selection now stores only top-level shelves in `genre`
+  (subgenres become tags mapped to their parent shelf; unknown-only
+  input leaves `genre` empty). Existing rows are unaffected until a
+  rescan/re-extract.
+