Fix Discography Backfill silently skipping most releases

Two bugs kept this job from finding anything useful on a typical library.

1. Wrong Deezer column name. The artists table has a deezer_id column
   (per music_database.py:1986), but the job looked for deezer_artist_id
   in both _scan_artist (line 132) and _get_library_artists (line 345).
   For Deezer-primary users, this meant the Deezer ID never made it into
   the source_ids map, so get_artist_discography fell back to artist-
   name-only search — slower and less accurate than an ID lookup.

2. Spotify-reported EPs were silently excluded. Spotify lumps EPs and
   true singles under album_type='single'. The previous
   _should_include_release short-circuited on album_type='single' and
   returned the include_singles setting (default False), so 4-6 track
   EPs on Spotify-primary libraries never survived the filter — even
   though include_eps defaulted to True. Only 7+ track full albums
   made it through. This is the main reason users felt the job did
   nothing.

Fixes:

- Use the correct deezer_id column name in both reference sites.

- Restructure _should_include_release so only 'album', 'ep', and
  'compilation' are trusted outright. Anything else (including
  'single' and missing type) falls through to a track-count
  disambiguation matching the download pipeline's _get_album_type_display:
  1-3 tracks = true single, 4-6 = EP, 7+ = album. A Spotify-returned
  'single' with 5 tracks now correctly counts as an EP.

Full suite stays at 263 passed. Ruff clean.

core/repair_jobs/discography_backfill.py

@@ -128,8 +128,8 @@ class DiscographyBackfillJob(RepairJob):
             source_ids['spotify'] = artist['spotify_artist_id']
         if artist.get('itunes_artist_id'):
             source_ids['itunes'] = artist['itunes_artist_id']
-        if artist.get('deezer_artist_id'):
-            source_ids['deezer'] = artist['deezer_artist_id']
+        if artist.get('deezer_id'):
+            source_ids['deezer'] = artist['deezer_id']
 
         # Fetch full discography
         discography = get_artist_discography(
@@ -294,21 +294,29 @@ class DiscographyBackfillJob(RepairJob):
 
     @staticmethod
     def _should_include_release(total_tracks, album_type, settings):
-        """Check if a release should be included based on type settings."""
-        # Use album_type from metadata source when available
+        """Check if a release should be included based on type settings.
+
+        Spotify lumps both EPs and true singles under album_type='single', so
+        only an explicit 'album' / 'ep' / 'compilation' is trusted outright.
+        Anything else (including 'single' or missing type) falls through to a
+        track-count disambiguation matching the download pipeline:
+          - 1-3 tracks -> true single
+          - 4-6 tracks -> EP
+          - 7+ tracks -> album
+        """
         normalized = (album_type or '').lower()
         if normalized == 'compilation':
             return settings.get('include_compilations', False)
-        if normalized in ('single',):
-            return settings.get('include_singles', False)
-        if normalized in ('ep',):
+        if normalized == 'album':
+            return settings.get('include_albums', True)
+        if normalized == 'ep':
             return settings.get('include_eps', True)
-        # Fall back to track count heuristic
+        # 'single' or missing: disambiguate by track count
         if total_tracks >= 7:
             return settings.get('include_albums', True)
-        elif total_tracks >= 4:
+        if total_tracks >= 4:
             return settings.get('include_eps', True)
-        elif total_tracks >= 1:
+        if total_tracks >= 1:
             return settings.get('include_singles', False)
         return settings.get('include_albums', True)
 
@@ -342,8 +350,8 @@ class DiscographyBackfillJob(RepairJob):
                 select.append("spotify_artist_id")
             if 'itunes_artist_id' in columns:
                 select.append("itunes_artist_id")
-            if 'deezer_artist_id' in columns:
-                select.append("deezer_artist_id")
+            if 'deezer_id' in columns:
+                select.append("deezer_id")
 
             cursor.execute(f"""
                 SELECT {', '.join(select)}