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

frontend/src/pages/admin/CreateEventPage.tsx

@@ -63,6 +63,8 @@ interface FormData {
   // Client access (#172)
   client_access_enabled: boolean;
   client_password: string;
+  // Default photo sort
+  default_photo_sort: string;
 }
 
 // Fallback event types (used when API is unavailable)
@@ -120,6 +122,7 @@ export const CreateEventPage: React.FC = () => {
     },
     client_access_enabled: false,
     client_password: '',
+    default_photo_sort: 'upload_date_desc',
   });
 
   const [errors, setErrors] = useState<Partial<Record<keyof FormData, string>>>({});
@@ -319,6 +322,8 @@ export const CreateEventPage: React.FC = () => {
       // Client access (#172)
       client_access_enabled: formData.client_access_enabled,
       client_password: formData.client_access_enabled ? formData.client_password : undefined,
+      // Default photo sort
+      default_photo_sort: formData.default_photo_sort,
     };
 
     createMutation.mutate(payload);
@@ -751,6 +756,25 @@ export const CreateEventPage: React.FC = () => {
               </div>
             </div>
 
+            {/* Default Photo Sort */}
+            <div className="pt-4 border-t border-neutral-200 dark:border-neutral-700">
+              <label className="block text-sm font-medium text-neutral-700 dark:text-neutral-300 mb-2">
+                {t('photoSort.defaultSort', 'Default Photo Sort')}
+              </label>
+              <select
+                value={formData.default_photo_sort}
+                onChange={(e) => setFormData({ ...formData, default_photo_sort: e.target.value })}
+                className="w-full px-3 py-2 border border-neutral-300 dark:border-neutral-600 bg-white dark:bg-neutral-800 text-neutral-900 dark:text-neutral-100 rounded-lg focus:ring-2 focus:ring-primary-500 focus:border-primary-500"
+              >
+                <option value="upload_date_desc">{t('photoSort.uploadDateNewest', 'Upload Date (Newest First)')}</option>
+                <option value="upload_date_asc">{t('photoSort.uploadDateOldest', 'Upload Date (Oldest First)')}</option>
+                <option value="capture_date_desc">{t('photoSort.captureDateNewest', 'Date Taken (Newest First)')}</option>
+                <option value="capture_date_asc">{t('photoSort.captureDateOldest', 'Date Taken (Oldest First)')}</option>
+                <option value="filename_asc">{t('photoSort.filenameAZ', 'Filename (A-Z)')}</option>
+                <option value="filename_desc">{t('photoSort.filenameZA', 'Filename (Z-A)')}</option>
+              </select>
+            </div>
+
             {/* Client Access (#172) */}
             <div className="pt-4 border-t border-neutral-200 dark:border-neutral-700">
               <label className="flex items-start gap-2">

frontend/src/pages/admin/EventDetailsPage.tsx

@@ -176,6 +176,8 @@ export const EventDetailsPage: React.FC = () => {
     hero_image_anchor: string;
     // Photo cap
     photo_cap: number;
+    // Default photo sort
+    default_photo_sort: string;
   };
 
   const [isEditing, setIsEditing] = useState(false);
@@ -209,6 +211,8 @@ export const EventDetailsPage: React.FC = () => {
     hero_image_anchor: 'center',
     // Photo cap
     photo_cap: 0,
+    // Default photo sort
+    default_photo_sort: 'upload_date_desc',
   });
   const [feedbackSettings, setFeedbackSettings] = useState<FeedbackSettingsType>({
     feedback_enabled: false,
@@ -442,6 +446,8 @@ export const EventDetailsPage: React.FC = () => {
       hero_image_anchor: event.hero_image_anchor || 'center',
       // Photo cap
       photo_cap: event.photo_cap || 0,
+      // Default photo sort
+      default_photo_sort: event.default_photo_sort || 'upload_date_desc',
     });
 
     setShowNewPassword(false);
@@ -577,6 +583,8 @@ export const EventDetailsPage: React.FC = () => {
       hero_image_anchor: editForm.hero_image_anchor,
       // Photo cap
       photo_cap: editForm.photo_cap > 0 ? editForm.photo_cap : null,
+      // Default photo sort
+      default_photo_sort: editForm.default_photo_sort,
       // Header style settings (decoupled from layout, #158)
       header_style: currentTheme?.headerStyle || 'standard',
       hero_divider_style: currentTheme?.heroDividerStyle || 'wave',
@@ -1125,6 +1133,25 @@ export const EventDetailsPage: React.FC = () => {
                   </div>
                 </div>
 
+                {/* Default Photo Sort */}
+                <div>
+                  <label className="block text-sm font-medium text-neutral-700 dark:text-neutral-300 mb-1">
+                    {t('photoSort.defaultSort', 'Default Photo Sort')}
+                  </label>
+                  <select
+                    value={editForm.default_photo_sort}
+                    onChange={(e) => setEditForm(prev => ({ ...prev, default_photo_sort: e.target.value }))}
+                    className="w-full px-3 py-2 border border-neutral-300 dark:border-neutral-600 bg-white dark:bg-neutral-800 text-neutral-900 dark:text-neutral-100 rounded-lg focus:ring-2 focus:ring-primary-500 focus:border-primary-500"
+                  >
+                    <option value="upload_date_desc">{t('photoSort.uploadDateNewest', 'Upload Date (Newest First)')}</option>
+                    <option value="upload_date_asc">{t('photoSort.uploadDateOldest', 'Upload Date (Oldest First)')}</option>
+                    <option value="capture_date_desc">{t('photoSort.captureDateNewest', 'Date Taken (Newest First)')}</option>
+                    <option value="capture_date_asc">{t('photoSort.captureDateOldest', 'Date Taken (Oldest First)')}</option>
+                    <option value="filename_asc">{t('photoSort.filenameAZ', 'Filename (A-Z)')}</option>
+                    <option value="filename_desc">{t('photoSort.filenameZA', 'Filename (Z-A)')}</option>
+                  </select>
+                </div>
+
                 <div>
                   <label className="flex items-center">
                     <input