Real backends + fetch/display workflows; config paths

Wire the incremental pipeline to real sources and expose two workflows.

Config (Env.py): three explicit paths — LOCAL_LIBRARY_PATH (scan source),
ITUNES_XML_PATH (manual export), DATA_DIR (storage root: DB + Spotify cache).

Real, incremental ingesters:
- local_scan: walks the library, skips files whose mtime/size are unchanged,
  prunes deleted ones, and reads embedded ISRC + recording MBID from tags
  (tagged files get real IDs with no network), via tags.py.
- itunes_xml: parse the iTunes Library.xml as a plist; skip if mtime unchanged.
- spotify_raw: ingest raw Spotify JSON (ISRC from external_ids); live fetch
  wrapper for when credentials are set.

Workflows (src/workflows.py + main.py):
- `fetch`  — pull + scan + parse + enrich + match, with readable step logs.
  First run is slow (full scan + MB lookups); later runs only touch changes
  (verified: ~71s first, ~0.6s second).
- `display` — launch the GUI.

Also: enrich uses ISRC-first again (local MBIDs now come from tags), fix
--enrich-limit 0, quiet musicbrainzngs XML warnings, ignore /data/.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -5,6 +5,7 @@ secret
 .env
 .venv
 *.db
+/data/
 work_dir
 old
 tmp