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>

Env.py

@@ -1,25 +1,39 @@
+"""Configuration. The three things you point at your own data:
+
+  LOCAL_LIBRARY_PATH  folder of audio files to scan
+  ITUNES_XML_PATH     iTunes/Music "Library.xml" you exported manually
+  DATA_DIR            storage root: the database + cached fetches live here
+
+Everything can be overridden via environment variables (see .env.example).
+"""
 import os
 from pathlib import Path
 
-# Local config. Paths can be overridden via environment variables.
-local_library_path = Path(os.environ.get("MUSIC_LIBRARY_PATH", "~/Music")).expanduser()
-work_dir = Path(os.environ.get("WORK_DIR", "./work_dir/new"))
 
-# Spotify app credentials. NEVER hardcode these here — set them in the
-# environment (see .env.example) so they don't end up in version control.
-#   export SPOTIFY_CLIENT_ID=...
-#   export SPOTIFY_CLIENT_SECRET=...
+def _path(env, default):
+    return Path(os.environ.get(env, default)).expanduser()
+
+
+# --- where YOUR data is read from / written to -------------------------------
+# Local music library to scan (tags incl. ISRC/MusicBrainz id are read).
+local_library_path = _path("LOCAL_LIBRARY_PATH", "~/Music")
+
+# iTunes / Apple Music library export. In the Music app:
+# File -> Library -> Export Library…  (produces an XML/plist file).
+itunes_xml_path = _path("ITUNES_XML_PATH", "~/Music/iTunes Library.xml")
+
+# Storage root — the database and cached Spotify responses go here.
+data_dir = _path("DATA_DIR", "./data")
+
+# --- derived storage locations -----------------------------------------------
+spotify_cache_dir = data_dir / "spotify"   # raw Spotify API responses
+database_url = os.environ.get(
+    "DATABASE_URL", f"sqlite:///{(data_dir / 'musicindexer.db').as_posix()}"
+)
+
+# --- Spotify app credentials (only needed for live fetching) -----------------
 client_id = os.environ.get("SPOTIFY_CLIENT_ID")
 client_secret = os.environ.get("SPOTIFY_CLIENT_SECRET")
 
-# Persistent store. Defaults to a local SQLite file; point DATABASE_URL at a
-# Postgres instance (postgresql+psycopg://user:pass@host/db) to switch with no
-# code changes.
-database_url = os.environ.get("DATABASE_URL", "sqlite:///./musicindexer.db")
-
-# Folder of prefetched JSON used to (re)build the DB without hitting the network.
-prefetched_dir = Path(os.environ.get("PREFETCHED_DIR", "./work_dir/latest-1"))
-
-# Contact email sent to MusicBrainz in the User-Agent (be a good API citizen).
+# Contact string sent to MusicBrainz in the User-Agent.
 mb_contact = os.environ.get("MB_CONTACT", "music-indexer@example.com")
-