CRITICAL: Fix database upsert bug preventing manual scan date persistence

**Root Cause**: upsert_movie_dates() was UPDATE-only, not proper upsert
- Manual scans failed to save dateadded to database (NULL values)
- Webhooks found database entries but with NULL dateadded
- Fell back to current timestamp instead of using proper import dates

**Database Fix**:
- Changed core/database.py upsert_movie_dates() from UPDATE to INSERT OR REPLACE
- Now properly saves dateadded during manual scans
- Preserves existing path with COALESCE fallback

**Webhook Enhancement**:
- Added comprehensive debug logging for database lookups
- Enhanced webhook date decision logic with proper fallback chain
- Only uses current timestamp as absolute last resort

**Impact**:
- Movies: Manual scans now persist dates, webhooks find existing entries ✅
- TV Shows: Not affected - already using proper INSERT OR REPLACE ✅
- Version: 1.5.5

VERSION

@@ -1 +1 @@
-1.5.3
+1.5.5