feat(roms): filter games by matched metadata provider

[Spinnich]

Description

Resolves #3439. Adds a Metadata provider gallery filter so a library can be
narrowed by which providers each game matched (IGDB, MobyGames, ScreenScraper,
RetroAchievements, LaunchBox, Hasheous, Flashpoint, HowLongToBeat, ES-DE,
Libretro), mirroring the existing multi-value filters (Player count, Age rating)
with the same any / all / none logic toggle.

The filter is exposed everywhere the other multi-value filters already live:
the classic (v1) and v2 gallery filter drawers, bookmarkable URL state, the
request cache key, and smart-collection create/serialize/summary. Provider
values are slugs that line up 1:1 across the backend column map, the shared
frontend options registry, and the MetadataSource enum.

Why static options? Unlike genres/age-ratings, the provider set is a fixed
enum, not derived from library content, so the drawer always offers all 10. This
is intentional and supports the curation use case in the issue (e.g. find games
with no IGDB match by selecting IGDB + none).

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Files modified

Backend

• backend/handler/database/roms_handler.py — METADATA_PROVIDER_COLUMNS slug→column map and _filter_by_metadata_providers (any=OR, all=AND, none=NOT-OR over each provider's id column); wired through filter_roms and get_roms_scalar. Unknown slugs are ignored.
• backend/endpoints/roms/__init__.py — metadata_providers + metadata_providers_logic query params on GET /roms, passed to filter_roms, and added to the unscoped-cache gate.
• backend/handler/database/collections_handler.py — smart collections apply the criterion via get_smart_collection_roms. NOTE: this file was the only CRLF file in the backend; it has been normalized to LF, which is why its diff is large (it's almost entirely line-ending).
• backend/tests/handler/test_db_handler.py — handler filter coverage (any/all/none + unknown-slug no-op).
• backend/tests/endpoints/roms/test_rom.py — endpoint coverage (filter + none logic).
• backend/tests/handler/database/test_collections_handler.py — smart-collection pass-through coverage.

Frontend (shared)

• frontend/src/utils/index.ts — shared METADATA_PROVIDER_OPTIONS registry (slug + brand-name title) used by both UIs.
• frontend/src/stores/galleryFilter.ts — selectedMetadataProviders / metadataProvidersLogic state, setters, isFiltered() / resetFilters().
• frontend/src/services/api/rom.ts — metadata_providers request params.
• frontend/src/services/cache/api.ts — provider selection folded into the request cache key (prevents stale-cache collisions).

Frontend (v1 classic UI)

• frontend/src/stores/roms.ts — passes the new filter to getRoms.
• frontend/src/components/Gallery/AppBar/common/FilterDrawer/Base.vue — new drawer row + URL read/write.

Frontend (v2 UI)

• frontend/src/v2/stores/galleryRoms.ts — passes the new filter to getRoms.
• frontend/src/v2/components/Gallery/FilterDrawer.vue — new multi-select section (slugs as values, brand names as titles) + logic toggle.
• frontend/src/v2/components/Gallery/GalleryShell.vue — added to the refetch watcher and active-filter count.
• frontend/src/v2/composables/useGalleryFilterUrl/index.ts — ?metadataProviders=…&metadataProvidersLogic=… URL round-trip (v1↔v2 compatible).
• frontend/src/v2/utils/smartCollectionCriteria.ts — serialization + human-readable summary field.
• frontend/src/v2/components/Dialogs/CreateSmartCollectionDialog.vue — snapshot includes the new fields.
• frontend/src/v2/utils/smartCollectionCriteria.test.ts — new unit tests (serialization + summary).

i18n

• frontend/src/locales/*/platform.json (18 locales) — platform.metadata-provider key (translated; parity check passes).

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Testing notes

• Backend full suite: 1793 passed (run with -p no:randomly for deterministic ordering).
• Frontend: 443 passed; vue-tsc typecheck clean.
• trunk fmt && trunk check: no issues. check_i18n_locales.py: all complete.
• New tests cover any/all/none logic, the unknown-slug no-op, the endpoint, the smart-collection pass-through, and smart-collection serialization/summary.
• If you see test_filter_by_search_term_* fail in a random-ordered run, it's pre-existing InnoDB MATCH...AGAINST flakiness (passes deterministically and in isolation; unrelated to this change).
• Not done: manual browser pass of the v2 drawer in both themes / all input modalities.

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Reviewer attention

1. Provider set vs the "Show matched" toggle. This filter's 10 providers align with the on-card chip registry (metadataProviders.ts) — what users actually see next to a ROM — which excludes tgdb/sgdb and includes hltb/gamelist/libretro. The existing _filter_by_matched toggle uses a different 8-provider set (includes tgdb, excludes hltb/gamelist/libretro). Please confirm aligning the filter with the chip registry (rather than the toggle) is the intended mapping.
2. Static options, not from filter_values — all 10 providers always show even on platforms with zero matches for some.
3. Smart collections: metadata_providers is now wired into get_smart_collection_roms; player_counts remains a pre-existing gap there and was intentionally left out of scope.
4. collections_handler.py CRLF→LF: review with whitespace hidden (?w=1) — the logical change is just 2 added lines.
5. No OpenAPI regen needed: no response schema changed (RomFiltersDict is untouched); request params are built manually in rom.ts.

AI assistance disclosure: this change was implemented with Claude Code (Anthropic), reviewed by the author.

Checklist

• I've tested the changes locally (full backend + frontend suites, trunk, i18n)
• I've updated relevant comments
• I've assigned reviewers for this PR
• I've added unit tests that cover the changes