fix: add thumbnail cleanup on archive deletion and diagnostic scripts

- Fix archive deletion to also clean up associated thumbnails
- Add cleanup-thumbnails.js script to remove temporary and orphaned thumbnails
- Add diagnose-thumbnails.js script to troubleshoot thumbnail serving issues
- Update README with documentation for new scripts

This prevents thumbnail accumulation when events are deleted and helps
diagnose why thumbnails might not be showing despite existing on disk.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/scripts/README.md

@@ -61,4 +61,43 @@ On your production server:
    NODE_ENV=production node scripts/regenerate-thumbnails.js 2
    ```
 
-Note: Replace `2` with the actual event ID from your database.
+Note: Replace `2` with the actual event ID from your database.
+
+## cleanup-thumbnails.js
+
+Cleans up temporary and orphaned thumbnail files.
+
+### Usage:
+```bash
+# Dry run - see what would be deleted
+node scripts/cleanup-thumbnails.js --dry-run
+
+# Actually delete orphaned thumbnails
+node scripts/cleanup-thumbnails.js
+```
+
+### What it does:
+- Identifies temporary thumbnails (thumb_temp_*)
+- Finds orphaned thumbnails not linked to any photo
+- Removes unnecessary files to free up space
+- Reports statistics on cleanup
+
+## diagnose-thumbnails.js
+
+Diagnoses why thumbnails might not be showing for a specific event.
+
+### Usage:
+```bash
+node scripts/diagnose-thumbnails.js 2
+```
+
+### What it checks:
+- Thumbnail paths in database vs filesystem
+- Path format inconsistencies
+- Missing thumbnail files
+- Provides SQL to fix path issues
+
+### Common Issues:
+1. **Path mismatch**: Database has wrong thumbnail path format
+2. **Missing files**: Thumbnails were never generated
+3. **Permission issues**: Web server can't read thumbnail files