feat(api): SHA-256 and Chromaprint fingerprints for the library (M5.5)

A background Fingerprinter runs after every scan and at startup, one file
at a time, filling media_files.sha256 and track_fingerprints (fpcalc raw,
first 120 s). Without fpcalc only SHA-256 is computed and files stay
queued for Chromaprint. Changing a file's content resets its prints.
Similarity() compares raw prints with a ±80-point alignment search; it is
the basis for duplicate detection in the upload queue.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

services/api/internal/library/store.go

@@ -271,7 +271,12 @@ func (st *Store) SaveFile(ctx context.Context, sourceID, id uuid.UUID, d FileDat
 			mtime = EXCLUDED.mtime, content_hash = EXCLUDED.content_hash, format = EXCLUDED.format,
 			codec = EXCLUDED.codec, bitrate = EXCLUDED.bitrate, sample_rate = EXCLUDED.sample_rate,
 			bit_depth = EXCLUDED.bit_depth, channels = EXCLUDED.channels, duration_ms = EXCLUDED.duration_ms,
-			track_id = EXCLUDED.track_id, scan_error = EXCLUDED.scan_error, missing_since = NULL`,
+			track_id = EXCLUDED.track_id, scan_error = EXCLUDED.scan_error, missing_since = NULL,
+			-- Содержимое изменилось — отпечатки посчитаются заново.
+			sha256 = CASE WHEN media_files.content_hash IS DISTINCT FROM EXCLUDED.content_hash
+				OR media_files.size_bytes <> EXCLUDED.size_bytes THEN NULL ELSE media_files.sha256 END,
+			fingerprinted_at = CASE WHEN media_files.content_hash IS DISTINCT FROM EXCLUDED.content_hash
+				OR media_files.size_bytes <> EXCLUDED.size_bytes THEN NULL ELSE media_files.fingerprinted_at END`,
 		id, sourceID, d.RelPath, d.Size, d.Mtime, d.ContentHash, p.Format, p.Codec, p.Bitrate, p.SampleRate,
 		p.BitDepth, p.Channels, p.DurationMs, trackID, scanErr)
 	if err != nil {
@@ -623,3 +628,58 @@ func (st *Store) WaveMetrics(ctx context.Context) (WaveMetrics, error) {
 	}
 	return m, nil
 }
+
+// FingerprintTodo — файл, которому нужны отпечатки.
+type FingerprintTodo struct {
+	ID       uuid.UUID
+	SourceID uuid.UUID
+	RelPath  string
+	SHA256   []byte // уже посчитан — повторно не читаем
+}
+
+// FilesToFingerprint — файлы смонтированных источников без SHA-256 (и без Chromaprint, если withFP), после after.
+func (st *Store) FilesToFingerprint(ctx context.Context, withFP bool, after uuid.UUID, limit int) ([]FingerprintTodo, error) {
+	rows, err := st.pool.Query(ctx, `
+		SELECT mf.id, mf.source_id, mf.rel_path, mf.sha256
+		FROM media_files mf
+		JOIN library_sources s ON s.id = mf.source_id AND s.status = 'mounted'
+		WHERE mf.missing_since IS NULL AND mf.scan_error IS NULL
+			AND (mf.sha256 IS NULL OR ($1 AND mf.fingerprinted_at IS NULL)) AND mf.id > $2
+		ORDER BY mf.id
+		LIMIT $3`, withFP, after, limit)
+	if err != nil {
+		return nil, fmt.Errorf("library: files to fingerprint: %w", err)
+	}
+	return pgx.CollectRows(rows, func(r pgx.CollectableRow) (FingerprintTodo, error) {
+		var f FingerprintTodo
+		return f, r.Scan(&f.ID, &f.SourceID, &f.RelPath, &f.SHA256)
+	})
+}
+
+// SaveFingerprint сохраняет SHA-256 и (если есть) отпечаток Chromaprint; chromaprintDone — fpcalc отработал
+// (в том числе с ошибкой), повторять не нужно.
+func (st *Store) SaveFingerprint(ctx context.Context, fileID uuid.UUID, sum []byte, fp *Fingerprint, chromaprintDone bool) error {
+	tx, err := st.pool.Begin(ctx)
+	if err != nil {
+		return fmt.Errorf("library: save fingerprint: %w", err)
+	}
+	defer func() { _ = tx.Rollback(ctx) }()
+	if _, err := tx.Exec(ctx, `
+		UPDATE media_files SET sha256 = $2, fingerprinted_at = CASE WHEN $3 THEN now() ELSE fingerprinted_at END
+		WHERE id = $1`, fileID, sum, chromaprintDone); err != nil {
+		return fmt.Errorf("library: save fingerprint: %w", err)
+	}
+	if fp != nil {
+		points := make([]int32, len(fp.Points))
+		for i, p := range fp.Points {
+			points[i] = int32(p)
+		}
+		if _, err := tx.Exec(ctx, `
+			INSERT INTO track_fingerprints (file_id, duration_ms, fingerprint, fp_prefix) VALUES ($1, $2, $3, $4)
+			ON CONFLICT (file_id) DO UPDATE SET duration_ms = EXCLUDED.duration_ms, fingerprint = EXCLUDED.fingerprint,
+				fp_prefix = EXCLUDED.fp_prefix`, fileID, fp.DurationMs, points, fp.Prefix()); err != nil {
+			return fmt.Errorf("library: save fingerprint: %w", err)
+		}
+	}
+	return tx.Commit(ctx)
+}