feat(server,web/m7-cover-sources): scan-orchestrator 4th stage

Adds an artist-art-enrich stage after cover-enrich in RunScan. The
stage drains EnrichArtistBatch with a configurable cap and the
operator's data_dir, persists processed/succeeded/failed tallies to
the scan_runs.artist_art_enrich jsonb column added in migration
0018.

The admin /admin Library Scan card grid expands from 3 to 4 columns
with the new "Artist art" card mirroring the cover-enrichment one
(Processed / Succeeded / Failed). The TS ScanStatus type gains an
optional artist_art_enrich field. The Go scanStatusResp gains the
matching ArtistArtEnrich json.RawMessage field.

cmd/minstrel/main.go (and admin scan-trigger handler) wire the new
RunScanConfig fields: ArtistEnrichCap reuses cfg.Library.CoverArtBackfillCap
for now (can be split if separate budgets are useful), DataDir is
cfg.Storage.DataDir.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/db/dbq/scan_runs.sql.go

@@ -53,20 +53,21 @@ func (q *Queries) GetInFlightScanRun(ctx context.Context) (GetInFlightScanRunRow
 }
 
 const getLatestScanRun = `-- name: GetLatestScanRun :one
-SELECT id, started_at, finished_at, library, mbid_backfill, cover_enrich, error_message
+SELECT id, started_at, finished_at, library, mbid_backfill, cover_enrich, artist_art_enrich, error_message
   FROM scan_runs
  ORDER BY started_at DESC
  LIMIT 1
 `
 
 type GetLatestScanRunRow struct {
-	ID           pgtype.UUID
-	StartedAt    pgtype.Timestamptz
-	FinishedAt   pgtype.Timestamptz
-	Library      []byte
-	MbidBackfill []byte
-	CoverEnrich  []byte
-	ErrorMessage *string
+	ID              pgtype.UUID
+	StartedAt       pgtype.Timestamptz
+	FinishedAt      pgtype.Timestamptz
+	Library         []byte
+	MbidBackfill    []byte
+	CoverEnrich     []byte
+	ArtistArtEnrich []byte
+	ErrorMessage    *string
 }
 
 // Powers GET /api/admin/scan/status. Returns NoRows when no scan has
@@ -81,6 +82,7 @@ func (q *Queries) GetLatestScanRun(ctx context.Context) (GetLatestScanRunRow, er
 		&i.Library,
 		&i.MbidBackfill,
 		&i.CoverEnrich,
+		&i.ArtistArtEnrich,
 		&i.ErrorMessage,
 	)
 	return i, err
@@ -106,6 +108,23 @@ func (q *Queries) InsertScanRun(ctx context.Context) (InsertScanRunRow, error) {
 	return i, err
 }
 
+const updateScanRunArtistArtEnrich = `-- name: UpdateScanRunArtistArtEnrich :exec
+UPDATE scan_runs
+   SET artist_art_enrich = $2
+ WHERE id = $1
+`
+
+type UpdateScanRunArtistArtEnrichParams struct {
+	ID              pgtype.UUID
+	ArtistArtEnrich []byte
+}
+
+// M7 cover-sources: persists the artist-art enrich stage tally JSON.
+func (q *Queries) UpdateScanRunArtistArtEnrich(ctx context.Context, arg UpdateScanRunArtistArtEnrichParams) error {
+	_, err := q.db.Exec(ctx, updateScanRunArtistArtEnrich, arg.ID, arg.ArtistArtEnrich)
+	return err
+}
+
 const updateScanRunCoverEnrich = `-- name: UpdateScanRunCoverEnrich :exec
 UPDATE scan_runs SET cover_enrich = $2 WHERE id = $1
 `