feat(db/m7-art-providers): migration 0020 + provider-hash queries

Relaxes the artists/albums art_source CHECK constraints to allow the
new 'deezer' and 'lastfm' source values alongside the existing
accepted set. Adds cover_art_sources_meta.last_registered_providers_hash
for the boot-time auto-bump detection: when the registered-provider
set changes between deploys, we bump current_version once so 'none'
rows become eligible for retry against the new chain.

Two sqlc queries added: GetCoverArtProvidersHash reads the stored
hash; BumpVersionAndSetProvidersHash atomically increments the
version and stores a new hash, returning the new version. Both used
by the boot logic in a later task.

internal/db/dbq/coverart_settings.sql.go

@@ -27,6 +27,38 @@ func (q *Queries) BumpSourcesVersion(ctx context.Context) (int32, error) {
 	return current_version, err
 }
 
+const bumpVersionAndSetProvidersHash = `-- name: BumpVersionAndSetProvidersHash :one
+UPDATE cover_art_sources_meta
+   SET current_version = current_version + 1,
+       last_registered_providers_hash = $1
+ WHERE id = true
+RETURNING current_version
+`
+
+// Atomically increments the version and stores the new provider-set
+// hash. Called at boot when the registered-provider set has changed
+// since the last start, so 'none' rows become eligible for retry.
+// RETURNING gives the new version without a follow-up SELECT.
+func (q *Queries) BumpVersionAndSetProvidersHash(ctx context.Context, lastRegisteredProvidersHash string) (int32, error) {
+	row := q.db.QueryRow(ctx, bumpVersionAndSetProvidersHash, lastRegisteredProvidersHash)
+	var current_version int32
+	err := row.Scan(&current_version)
+	return current_version, err
+}
+
+const getCoverArtProvidersHash = `-- name: GetCoverArtProvidersHash :one
+SELECT last_registered_providers_hash
+  FROM cover_art_sources_meta
+ WHERE id = true
+`
+
+func (q *Queries) GetCoverArtProvidersHash(ctx context.Context) (string, error) {
+	row := q.db.QueryRow(ctx, getCoverArtProvidersHash)
+	var last_registered_providers_hash string
+	err := row.Scan(&last_registered_providers_hash)
+	return last_registered_providers_hash, err
+}
+
 const getCurrentSourcesVersion = `-- name: GetCurrentSourcesVersion :one
 SELECT current_version FROM cover_art_sources_meta WHERE id = true
 `