feat: data lifecycle rewrite, download clients, wanted list, and central catalog index

Ships the fresh-start schema cleanup: rebuilt explore catalog index
pipeline (dump import, artifact fetch/build, incremental listen-count
refresh), a new download subsystem (Lidarr/Prowlarr/qBittorrent/SABnzbd/
slskd/yt-dlp providers, staging, reconciliation, wanted list), and the
supporting schema/query/store changes across backend and frontend.

Also includes two smaller follow-ups: bump the central index's
rebuild-after cadence from 90 to 180 days, and remove the Explore
"library only" online/offline toggle entirely (frontend-only, no
backend counterpart) rather than carry unused UI/state.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y2Agd9af5hE7qzti2ackiS

backend/tagwriter/dbsync.go

@@ -417,6 +417,26 @@ func syncDatabase(
 		}
 	}
 
+	// ------------------------------------------------------------------
+	// 7d. Re-baseline the staleness fields.  Writing tags rewrites the
+	//     file, changing its mtime and possibly its size.  Recording the
+	//     new values here keeps the scan from mistaking YellowJacket's
+	//     own edit for an external one and re-importing the track.
+	// ------------------------------------------------------------------
+	if info, statErr := os.Stat(params.filePath); statErr != nil {
+		logger.Warn("could not stat file after tag write",
+			"path", params.filePath, "err", statErr)
+	} else if updErr := txq.UpdateAudioFileStat(ctx,
+		sqlcgen.UpdateAudioFileStatParams{
+			ModifiedAt: info.ModTime().Unix(),
+			FileSize:   info.Size(),
+			ID:         params.audioFileID,
+		},
+	); updErr != nil {
+		logger.Warn("could not update file stat after tag write",
+			"path", params.filePath, "err", updErr)
+	}
+
 	// ------------------------------------------------------------------
 	// 8. Commit.
 	// ------------------------------------------------------------------

backend/tagwriter/pipeline.go

@@ -194,6 +194,51 @@ func (tw *TagWriter) WriteTrackTags(trackID int64, changes TagChanges) error {
 	return nil
 }
 
+// WriteUntrackedFileTags writes tags to a file that is not in the
+// library, skipping every step of the full pipeline that assumes it is:
+// no audio_file lookup, no database sync, no event.
+//
+// This exists for the download import path, which tags files while they
+// are still in the staging directory.  Tagging before the move is what
+// makes the import atomic from the library's point of view — the
+// scanner only ever sees a finished, correctly tagged file, instead of
+// ingesting a mislabelled one and being corrected afterwards.
+//
+// Callers are responsible for ensuring the file is not in a library
+// path; using this on a tracked file would leave the database stale.
+func (tw *TagWriter) WriteUntrackedFileTags(
+	filePath string,
+	changes TagChanges,
+) error {
+	if len(changes) == 0 {
+		return errNoChanges
+	}
+
+	format, err := DetectFormat(filePath)
+	if err != nil {
+		return fmt.Errorf("detect format: %w", err)
+	}
+
+	switch format {
+	case FormatMP3:
+		err = writeMp3Tags(tw.logger, filePath, changes)
+	case FormatFLAC:
+		err = writeFlacTags(tw.logger, filePath, changes)
+	case FormatWAV:
+		err = writeWavTags(tw.logger, filePath, changes)
+	case FormatOGG:
+		err = writeOggTags(tw.logger, filePath, changes)
+	default:
+		err = fmt.Errorf("%w: %s", errUnsupportedFormat, format)
+	}
+
+	if err != nil {
+		return fmt.Errorf("write file tags: %w", err)
+	}
+
+	return nil
+}
+
 // WriteTrackTagsByPath resolves a file path to its audio_file.id and
 // delegates to WriteTrackTags.  This is the frontend-facing entry
 // point since the frontend identifies tracks by FilePath.