fix(spotify): reduce API rate limiting by lowering pagination and increasing interval

Spotify enforces undocumented hourly rate limits that trigger 429 errors after
~50 paginated API calls. Two changes to prevent hitting these limits:

1. Reduced max_pages from 5 to 2 in spotify_worker _process_album_batch
   - Cuts pagination calls by 60% (5→2 pages per artist)
   - Still fetches 20 newest albums, sufficient for most libraries

2. Increased MIN_API_INTERVAL from 0.35s to 0.70s
   - Reduces calls from ~171/min to ~85/min
   - Provides larger safety margin before rate limits trigger

Both changes maintain full functionality - unmatched albums fall back to iTunes.

core/spotify_client.py

@@ -14,7 +14,7 @@ logger = get_logger("spotify_client")
 # Global rate limiting variables
 _last_api_call_time = 0
 _api_call_lock = threading.Lock()
-MIN_API_INTERVAL = 0.35  # Default: 350ms between API calls (~171/min, under Spotify's ~180/min limit)
+MIN_API_INTERVAL = 0.70  # Default: 350ms between API calls (~171/min, under Spotify's ~180/min limit)
 
 def _get_min_api_interval():
     """Get configurable API interval from settings, falling back to default."""

core/spotify_worker.py

@@ -491,13 +491,14 @@ class SpotifyWorker:
         spotify_artist_id = item['spotify_artist_id']
         artist_name = item['artist_name']
 
-        # Fetch albums with pagination cap — Spotify returns 10/page, so max_pages=5
-        # gives 50 albums (newest first). Avoids 20+ paginated calls for prolific artists
-        # (e.g., 217 albums = 22 API calls without cap, vs 5 with cap)
+        # Fetch albums with pagination cap — Spotify returns 10/page, so max_pages=2
+        # gives 20 albums (newest first). Most libraries have <20 albums per artist.
+        # Reduced from max_pages=5 to avoid Spotify's undocumented hourly rate limits
+        # which trigger after ~50 paginated calls (10 artists × 5 pages = 50 calls).
         try:
             spotify_albums = self.client.get_artist_albums(
                 spotify_artist_id, album_type='album,single,compilation', limit=50,
-                max_pages=5
+                max_pages=2
             )
         except Exception as e:
             logger.error(f"Failed to get Spotify albums for artist '{artist_name}': {e}")