add tag-album and clean-playlist-files tasks, script step support, stop fix, rename fix

- New tag-album task: renames tracks to NNN format, sets ID3 tags via mutagen
- New clean-playlist-files task: deletes .cue, .m3u, .nfo and similar junk files
- Pipeline executor now supports script-mode steps (runs directly, no agent)
- Build discography pipeline: convert-audio → clean-playlist-files → prepare → fetch → tag
- Fix stop button: abort signal now kills running agent processes
- Fix job manager: broadcast stopped/error events to WebSocket viewers
- Fix file browser rename: delay focus to avoid context menu close race, left-align input

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

src/servers/api/tasks/pipeline-job-manager.ts

@@ -161,6 +161,7 @@ export async function startJob(params: StartJobParams): Promise<string> {
     clearInterval(flushInterval);
     const message = err instanceof Error ? err.message : String(err);
     const isStopped = job.abortSignal.aborted;
+    broadcast(job, isStopped ? { type: 'stopped' } : { type: 'error', message });
     await updatePipelineJob(jobId, {
       status: isStopped ? 'stopped' : 'failed',
       progress: job.lastProgress as Record<string, unknown>,