Add bulk import optimization: track_lookup cache, batch inserts, BulkSubmitter

internal/catalog/lookup_key.go

@@ -0,0 +1,9 @@
+package catalog
+
+import "strings"
+
+// TrackLookupKey builds a normalized cache key for entity resolution.
+// Uses null-byte separators to avoid collisions between field values.
+func TrackLookupKey(artist, track, album string) string {
+	return strings.ToLower(artist) + "\x00" + strings.ToLower(track) + "\x00" + strings.ToLower(album)
+}