feat: implement 4 new features with bug fixes and refactoring plan

## Features Implemented

### 1. Event Rename Functionality
- Add EventRenameDialog component with live slug preview
- Create eventRenameService for safe event renaming
- Add slug_redirects table for old URL redirects
- Support optional email notification on rename
- Fix date formatting in slug (YYYY-MM-DD format)

### 2. Optional Event Contact Fields
- Add settings to make customer name/email/admin email optional
- Create migration for field requirement settings
- Update CreateEventPage forms to show "(optional)" labels
- Fix boolean parsing in publicSettings.js

### 3. Photo Filtering & Export
- Add PhotoFilterPanel with rating/likes/favorites/comments filters
- Create PhotoExportMenu with ZIP/metadata/XMP export options
- Add photoExportService with Lightroom XMP sidecar generation
- Create photoFilterBuilder utility for query construction
- Wire up photo selection to export button via onSelectionChange

### 4. Custom CSS Gallery Templates
- Add CssTemplateEditor component with 3 template slots
- Create cssSanitizer utility blocking XSS vectors
- Add gallery CSS endpoint for template delivery
- Integrate Custom CSS tab into Settings page
- Include default "Elegant Dark" template

## Bug Fixes
- Fix event rename date formatting (was showing full Date string)
- Fix common.optional translation key missing in locales
- Fix photo export button staying disabled when photos selected
- Fix authService import missing in SettingsPage

## Documentation
- Add comprehensive REFACTORING_PLAN.md for codebase improvement
- Add test specification documents for all features
- Add feature documentation for CSS templates

## Database Migrations
- 049_add_slug_redirects.js
- 050_add_optional_event_fields_settings.js
- 051_add_photo_filter_indexes.js
- 052_add_css_templates.js

backend/server.js

@@ -432,6 +432,9 @@ app.use('/api/admin/feedback', require('./src/routes/adminFeedback'));
 app.use('/api/admin/image-security', require('./src/routes/adminImageSecurity'));
 app.use('/api/admin/thumbnails', require('./src/routes/adminThumbnails'));
 app.use('/api/admin/photos', require('./src/routes/adminPhotos'));
+app.use('/api/admin/photo-export', require('./src/routes/adminPhotoExport'));
+app.use('/api/admin/css-templates', require('./src/routes/adminCssTemplates'));
+app.use('/api/admin/events', require('./src/routes/adminEventRename'));
 app.use('/api/public/settings', require('./src/routes/publicSettings'));
 app.use('/api/public', require('./src/routes/publicCMS'));
 app.use('/api/images', require('./src/routes/protectedImages'));