Enhance email templates with clickable links, branding, and improved styling

- Add clickable gallery links in all email templates
- Include application logo in email header and footer (custom or PicPeak default)
- Redesign emails with professional styling matching gallery login page
  - Gray background with white content box
  - PicPeak green header with centered logo
  - Clean typography and proper spacing
  - Responsive design for mobile devices
  - Styled call-to-action buttons
  - Footer with branding and copyright
- Update email processor to fetch branding settings dynamically
- Use proper API URLs for logo images in emails

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

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

frontend/src/pages/admin/SettingsPage.tsx

@@ -56,7 +56,8 @@ export const SettingsPage: React.FC = () => {
     enable_analytics: true,
     enable_registration: false,
     maintenance_mode: false,
-    default_language: 'en'
+    default_language: 'en',
+    date_format: { format: 'DD/MM/YYYY', locale: 'en-GB' }
   });
 
   // Security settings state
@@ -88,7 +89,8 @@ export const SettingsPage: React.FC = () => {
         enable_analytics: settings.general_enable_analytics || true,
         enable_registration: settings.general_enable_registration || false,
         maintenance_mode: settings.general_maintenance_mode || false,
-        default_language: settings.general_default_language || 'en'
+        default_language: settings.general_default_language || 'en',
+        date_format: settings.general_date_format || { format: 'DD/MM/YYYY', locale: 'en-GB' }
       });
 
       // Extract security settings
@@ -337,6 +339,38 @@ export const SettingsPage: React.FC = () => {
                 </p>
               </div>
             </div>
+          </Card>
+
+          <Card padding="md">
+            <h2 className="text-lg font-semibold text-neutral-900 mb-4">{t('settings.general.dateTimeFormat')}</h2>
+            
+            <div className="space-y-4">
+              <div>
+                <label className="block text-sm font-medium text-neutral-700 mb-2">
+                  {t('settings.general.dateFormat')}
+                </label>
+                <select
+                  value={generalSettings.date_format?.format || 'DD/MM/YYYY'}
+                  onChange={(e) => {
+                    const format = e.target.value;
+                    const locale = format === 'MM/DD/YYYY' ? 'en-US' : 'en-GB';
+                    setGeneralSettings(prev => ({ 
+                      ...prev, 
+                      date_format: { format, locale }
+                    }));
+                  }}
+                  className="w-full px-3 py-2 border border-neutral-300 rounded-lg focus:outline-none focus:ring-2 focus:ring-primary-500 focus:border-primary-500"
+                >
+                  <option value="DD/MM/YYYY">DD/MM/YYYY (European)</option>
+                  <option value="MM/DD/YYYY">MM/DD/YYYY (US)</option>
+                  <option value="YYYY-MM-DD">YYYY-MM-DD (ISO)</option>
+                  <option value="DD.MM.YYYY">DD.MM.YYYY (German)</option>
+                </select>
+                <p className="text-xs text-neutral-500 mt-1">
+                  {t('settings.general.dateFormatHelp')}
+                </p>
+              </div>
+            </div>
 
             <div className="mt-6">
               <Button