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/library/scanrun.go

@@ -40,12 +40,22 @@ type CoverEnrichStageTallies struct {
 	Failed    int `json:"failed"`
 }
 
+// ArtistArtEnrichStageTallies wires EnrichArtistBatch tallies into
+// the scan_runs jsonb column.
+type ArtistArtEnrichStageTallies struct {
+	Processed int `json:"processed"`
+	Succeeded int `json:"succeeded"`
+	Failed    int `json:"failed"`
+}
+
 // RunScanConfig assembles the knobs for the orchestrator. BackfillCap and
 // EnrichCap mirror the existing boot-time caps (5000 / coverArtBackfillCap)
 // so manual triggers don't accidentally drain the whole library.
 type RunScanConfig struct {
-	BackfillCap int
-	EnrichCap   int
+	BackfillCap     int
+	EnrichCap       int
+	ArtistEnrichCap int    // M7 cover-sources: cap for the artist-art enrich stage
+	DataDir         string // M7 cover-sources: where to write artist-art files
 }
 
 // RunScan is the unified scan-chain orchestrator. Creates a scan_runs row,
@@ -131,6 +141,22 @@ func RunScan(
 		}
 	}
 
+	// Stage 4: artist art enrichment.
+	if enricher != nil && cfg.ArtistEnrichCap != 0 && cfg.DataDir != "" {
+		processed, succeeded, failed, ceerr := enricher.EnrichArtistBatch(ctx, cfg.ArtistEnrichCap, cfg.DataDir)
+		if ceerr != nil {
+			captureErr("artist_art_enrich", ceerr)
+		}
+		blob, _ := json.Marshal(ArtistArtEnrichStageTallies{
+			Processed: processed, Succeeded: succeeded, Failed: failed,
+		})
+		if uerr := q.UpdateScanRunArtistArtEnrich(ctx, dbq.UpdateScanRunArtistArtEnrichParams{
+			ID: row.ID, ArtistArtEnrich: blob,
+		}); uerr != nil {
+			captureErr("artist_art_enrich_persist", uerr)
+		}
+	}
+
 	// Finalize: set finished_at + error message (or empty string if all stages succeeded).
 	errMsg := ""
 	if firstErr != nil {