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.example

@@ -1,9 +1,18 @@
-# Copy to `.env` and fill in, then `source .env` before running.
-# Get these from https://developer.spotify.com/dashboard (your app's settings).
-# Register `http://127.0.0.1:8888` as a Redirect URI in that app.
+# Copy to `.env`, fill in, then `source .env` before running.
+
+# --- the three things you point at your own data ---------------------------
+# Folder of audio files to scan (tags incl. ISRC / MusicBrainz id are read).
+export LOCAL_LIBRARY_PATH=~/Music
+# iTunes/Music "Library.xml" you export manually (File > Library > Export Library…).
+export ITUNES_XML_PATH=~/Music/iTunes\ Library.xml
+# Storage root: the database and cached Spotify responses live here.
+export DATA_DIR=./data
+
+# --- Spotify credentials (only needed for live fetching) -------------------
+# https://developer.spotify.com/dashboard — register http://127.0.0.1:8888 as a Redirect URI.
 export SPOTIFY_CLIENT_ID=your_client_id_here
 export SPOTIFY_CLIENT_SECRET=your_client_secret_here
 
-# Optional overrides:
-# export MUSIC_LIBRARY_PATH=~/Music
-# export WORK_DIR=./work_dir/new
+# --- optional --------------------------------------------------------------
+# export MB_CONTACT=you@example.com                         # MusicBrainz User-Agent contact
+# export DATABASE_URL=postgresql+psycopg://u:p@localhost/mi # use Postgres instead of SQLite