feat(db/m7-cover-sources): SQL queries for provider settings + recheck

- Extends GetAlbumCoverageRollup's with_art FILTER to include
  'theaudiodb' so F's coverage gauge surfaces TheAudioDB-found rows
  as with_art rather than silently undercounting.
- Modifies ListAlbumsMissingCover to take the current sources_version
  as a parameter; eligibility now includes stale-'none' rows.
- Adds SetAlbumCoverWithVersion (atomic write of path + source +
  version stamp) and the parallel SetArtistArtWithVersion +
  ClearArtistArtNone + ListArtistsMissingArt for the artist-art
  enricher.
- New coverart_settings.sql with ListProviderSettings,
  UpsertProviderSettings (boot reconciliation, preserves operator
  values on conflict), UpdateProviderSettings (admin PATCH; tri-
  state api_key handling), GetCurrentSourcesVersion,
  BumpSourcesVersion (RETURNING the new value).

internal/db/queries/albums.sql

@@ -136,15 +136,26 @@ SELECT a.id          AS album_id,
 -- Invariant: with_art + pending + settled = total. (pending_no_mbid is
 -- not part of the sum — it's a subset of pending, surfaced separately.)
 --
--- The IN list below ('sidecar','embedded','mbcaa') must stay in sync
+-- The IN list below ('sidecar','embedded','mbcaa','theaudiodb') must stay in sync
 -- with the cover_art_source CHECK constraint in migration
 -- 0016_album_cover_source.up.sql. If a new source value is added there
 -- without updating this query, with_art will silently undercount.
 SELECT
   COUNT(*)                                                                   AS total,
-  COUNT(*) FILTER (WHERE cover_art_source IN ('sidecar','embedded','mbcaa')) AS with_art,
+  COUNT(*) FILTER (WHERE cover_art_source IN ('sidecar','embedded','mbcaa','theaudiodb')) AS with_art,
   COUNT(*) FILTER (WHERE cover_art_source IS NULL)                           AS pending,
   COUNT(*) FILTER (WHERE cover_art_source = 'none')                          AS settled,
   COUNT(*) FILTER (WHERE cover_art_source IS NULL AND mbid IS NULL)          AS pending_no_mbid
 FROM albums;
 
+-- name: SetAlbumCoverWithVersion :exec
+-- M7 cover-sources: records a successful or settled enrichment with the
+-- current sources_version stamp. cover_art_path is NULL when source is
+-- 'none' (no file written). Atomic; called per album per pass.
+UPDATE albums
+   SET cover_art_path            = $2,
+       cover_art_source          = $3,
+       cover_art_sources_version = $4,
+       updated_at                = now()
+ WHERE id = $1;
+