feat: Add dedicated failed movies debug log

- Create logs/failed_movies.log for movies with no_valid_date_source
- Logs movie name, IMDb ID, failure reason, and timestamp
- Helps users identify problematic movies needing manual attention
- Useful for debugging API issues and monitoring system health
- Documented in SUMMARY.md action items for troubleshooting workflow

.local/SUMMARY.md

@@ -204,6 +204,7 @@ Co-Authored-By: Claude <noreply@anthropic.com> ❌
 - **API Debug Endpoints**: `/debug/movie/{imdb_id}` for troubleshooting specific movies
 - **IMDb ID Detection**: Comprehensive logging for directory/filename/NFO parsing
 - **Three-Tier Logging**: Shows which optimization tier is used for each movie
+- **Failed Movies Log**: Dedicated `logs/failed_movies.log` for movies with no_valid_date_source
 
 ### 🎯 PERFORMANCE TESTING SCENARIOS
 - **Cold Database**: Test full processing with empty database (Tier 3 for all content)
@@ -252,6 +253,7 @@ Co-Authored-By: Claude <noreply@anthropic.com> ❌
 4. **TMDB FALLBACK TESTING**: Test movies with TMDB IDs but no IMDb IDs
 5. **MONITOR**: Database size should remain appropriate with new optimizations
 6. **BENCHMARK**: Compare scan times before/after optimization (should see 90%+ improvement)
+7. **DEBUG LOG**: Check `logs/failed_movies.log` for movies that couldn't get valid dates
 
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