feat: sort photos by capture date with configurable default sort (#283)

Add per-event default photo sort setting with 6 options:
- Upload Date (Newest/Oldest First)
- Date Taken (Newest/Oldest First) — uses EXIF captured_at
- Filename (A-Z / Z-A)

Backend:
- Migration 077 adds default_photo_sort column to events table
- Event create/update handlers accept and validate the setting
- Gallery info endpoint returns default_photo_sort for frontend

Frontend:
- "Date Taken" added to gallery sort dropdown (alongside Date, Name,
  Size, Rating)
- Gallery initializes with event's default sort instead of hardcoded
  "date"
- "Default Photo Sort" dropdown in event create and edit forms
- Photos without EXIF dates fall back to upload date

i18n: All 5 locales (EN, DE, NL, PT, RU) updated with sort labels.

Closes #283

backend/src/routes/adminEvents.js

@@ -259,7 +259,12 @@ router.post('/', adminAuth, requirePermission('events.create'), [
   body('hero_image_anchor').optional().custom(validateHeroImageAnchor),
   // Client access settings (#172)
   body('client_access_enabled').optional().isBoolean(),
-  body('client_password').optional().isString()
+  body('client_password').optional().isString(),
+  body('default_photo_sort').optional().isIn([
+    'upload_date_desc', 'upload_date_asc',
+    'capture_date_desc', 'capture_date_asc',
+    'filename_asc', 'filename_desc'
+  ])
 ], async (req, res) => {
   try {
     logger.debug('Create event request body', { body: req.body });
@@ -314,7 +319,9 @@ router.post('/', adminAuth, requirePermission('events.create'), [
       client_access_enabled = false,
       client_password = null,
       // Draft mode
-      is_draft = true
+      is_draft = true,
+      // Default photo sort
+      default_photo_sort = 'upload_date_desc'
     } = req.body;
 
     const customerName = getCustomerNameFromPayload(req.body);
@@ -483,6 +490,7 @@ router.post('/', adminAuth, requirePermission('events.create'), [
       hero_image_anchor: hero_image_anchor || 'center',
       photo_cap: photo_cap || null,
       is_draft: formatBoolean(parseBooleanInput(is_draft, true)),
+      default_photo_sort: default_photo_sort || 'upload_date_desc',
       // Client access (#172)
       client_access_enabled: formatBoolean(client_access_enabled),
       ...(client_access_enabled && client_password ? {
@@ -856,7 +864,12 @@ router.put('/:id', adminAuth, requirePermission('events.edit'), requireEventOwne
   // Client access settings (#172)
   body('client_access_enabled').optional().isBoolean(),
   body('client_password').optional().isString(),
-  body('regenerate_client_token').optional().isBoolean()
+  body('regenerate_client_token').optional().isBoolean(),
+  body('default_photo_sort').optional().isIn([
+    'upload_date_desc', 'upload_date_asc',
+    'capture_date_desc', 'capture_date_asc',
+    'filename_asc', 'filename_desc'
+  ])
 ], async (req, res) => {
   try {
     const errors = validationResult(req);

backend/src/routes/gallery.js

@@ -123,7 +123,8 @@ router.get('/:slug/info', async (req, res) => {
         'header_style',
         'hero_divider_style',
         'hero_image_anchor',
-        'is_draft'
+        'is_draft',
+        'default_photo_sort'
       )
       .first();
 
@@ -182,7 +183,8 @@ router.get('/:slug/info', async (req, res) => {
       hero_logo_url: event.hero_logo_url || null,
       header_style: event.header_style || 'standard',
       hero_divider_style: event.hero_divider_style || 'wave',
-      hero_image_anchor: event.hero_image_anchor || 'center'
+      hero_image_anchor: event.hero_image_anchor || 'center',
+      default_photo_sort: event.default_photo_sort || 'upload_date_desc'
     });
   } catch (error) {
     console.error('Error fetching gallery info:', error);
@@ -397,6 +399,7 @@ router.get('/:slug/photos', verifyGalleryAccess, async (req, res) => {
         header_style: req.event.header_style || 'standard',
         hero_divider_style: req.event.hero_divider_style || 'wave',
         hero_image_anchor: req.event.hero_image_anchor || 'center',
+        default_photo_sort: req.event.default_photo_sort || 'upload_date_desc',
         ...protectionSettings
       },
       categories: categories,