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;
+

internal/db/queries/artists.sql

@@ -11,7 +11,15 @@ DO UPDATE SET
 RETURNING *;
 
 -- name: GetArtistByID :one
-SELECT * FROM artists WHERE id = $1;
+-- M7 cover-sources: enricher reads the artist's mbid + current art
+-- columns to drive eligibility check. (Modified from SELECT * to
+-- explicitly include the new artist_art_* columns added in migration
+-- 0018.)
+SELECT a.id, a.name, a.sort_name, a.mbid,
+       a.artist_thumb_path, a.artist_fanart_path,
+       a.artist_art_source, a.artist_art_sources_version
+  FROM artists a
+ WHERE a.id = $1;
 
 -- name: GetArtistByName :one
 SELECT * FROM artists WHERE name = $1 LIMIT 1;
@@ -83,3 +91,38 @@ UPDATE artists
    SET mbid = $2,
        updated_at = now()
  WHERE id = $1 AND mbid IS NULL;
+
+-- name: ListArtistsMissingArt :many
+-- M7 cover-sources: returns artist rows the artist-art enricher should
+-- attempt. Eligible: artist_art_source IS NULL OR (= 'none' AND stale
+-- artist_art_sources_version). MBID-less artists are returned but the
+-- enricher skips them at the row.mbid == nil guard inside the chain.
+SELECT a.id
+  FROM artists a
+ WHERE a.artist_art_source IS NULL
+    OR (a.artist_art_source = 'none' AND a.artist_art_sources_version != $1)
+ ORDER BY a.created_at
+ LIMIT $2;
+
+-- name: SetArtistArtWithVersion :exec
+-- M7 cover-sources: records a successful or settled artist-art
+-- enrichment with the current sources_version stamp. thumb_path /
+-- fanart_path are NULL on a 'none' result, or independently NULL if
+-- the provider returned only one of the two image types (e.g.
+-- TheAudioDB had a thumb but no fanart for this artist).
+UPDATE artists
+   SET artist_thumb_path           = $2,
+       artist_fanart_path          = $3,
+       artist_art_source           = $4,
+       artist_art_sources_version  = $5,
+       updated_at                  = now()
+ WHERE id = $1;
+
+-- name: ClearArtistArtNone :exec
+-- M7 cover-sources: parallel of ClearAlbumCoverNone. Used by the
+-- eligibility loop to flip stale 'none' rows back to NULL.
+UPDATE artists
+   SET artist_art_source = NULL,
+       updated_at        = now()
+ WHERE id = $1
+   AND artist_art_source = 'none';

internal/db/queries/coverart_settings.sql

@@ -0,0 +1,46 @@
+-- M7 cover-sources: queries for the cover_art_provider_settings table
+-- and the cover_art_sources_meta singleton. The SettingsService
+-- consumes these.
+
+-- name: ListProviderSettings :many
+-- Returns all rows from cover_art_provider_settings. Used by the
+-- SettingsService at boot for reconciliation and by the admin GET
+-- handler.
+SELECT provider_id, enabled, api_key, display_order, created_at, updated_at
+  FROM cover_art_provider_settings
+ ORDER BY display_order, provider_id;
+
+-- name: UpsertProviderSettings :exec
+-- INSERT a default row for a newly-registered provider, or update an
+-- existing row's display_order on boot reconciliation. Does NOT
+-- overwrite enabled / api_key on conflict — the operator's settings
+-- persist across restarts.
+INSERT INTO cover_art_provider_settings (provider_id, enabled, display_order)
+VALUES ($1, $2, $3)
+ON CONFLICT (provider_id) DO UPDATE
+   SET display_order = EXCLUDED.display_order,
+       updated_at    = now();
+
+-- name: UpdateProviderSettings :exec
+-- Admin PATCH applies one or both fields. Pass NULL for enabled to
+-- leave it unchanged. Pass FALSE for the apiKeyChanged flag to leave
+-- the api_key unchanged regardless of apiKey value; pass TRUE with
+-- empty string to clear, or TRUE with non-empty to set.
+UPDATE cover_art_provider_settings
+   SET enabled    = COALESCE($2, enabled),
+       api_key    = CASE WHEN $3::boolean THEN $4 ELSE api_key END,
+       updated_at = now()
+ WHERE provider_id = $1;
+
+-- name: GetCurrentSourcesVersion :one
+SELECT current_version FROM cover_art_sources_meta WHERE id = true;
+
+-- name: BumpSourcesVersion :one
+-- Increments and returns the new version. Called by SettingsService
+-- only when the *enabled set* changes (not on key/display_order
+-- changes). RETURNING gives the new value back so the handler can
+-- include it in the response without a follow-up SELECT.
+UPDATE cover_art_sources_meta
+   SET current_version = current_version + 1
+ WHERE id = true
+RETURNING current_version;

internal/db/queries/covers.sql

@@ -1,13 +1,17 @@
 -- M7 #353: album cover enrichment queries.
 
 -- name: ListAlbumsMissingCover :many
--- Albums where cover_art_source has never been set. Used by the boot
--- backfill and post-scan enrichment passes. LIMIT supplied by caller.
-SELECT a.id, a.mbid, a.title, a.artist_id
+-- M7 cover-sources: returns rows the enricher should attempt. Eligible:
+-- cover_art_source IS NULL (never tried), OR cover_art_source = 'none'
+-- AND cover_art_sources_version != current (settled under an older
+-- source set; recheck against the current chain). LIMIT supplied by
+-- caller for batching.
+SELECT a.id
   FROM albums a
  WHERE a.cover_art_source IS NULL
- ORDER BY a.created_at ASC
- LIMIT $1;
+    OR (a.cover_art_source = 'none' AND a.cover_art_sources_version != $1)
+ ORDER BY a.created_at
+ LIMIT $2;
 
 -- name: ListAlbumsRetryMissing :many
 -- Bulk-retry candidates: NULL (never tried) plus 'none' (tried, failed).