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/components/admin/AdminSidebar.tsx

@@ -7,7 +7,6 @@ import {
   Archive, 
   BarChart3, 
   Settings,
-  Camera,
   X,
   Palette,
   FileText
@@ -53,7 +52,7 @@ export const AdminSidebar: React.FC<AdminSidebarProps> = ({ isOpen, onClose }) =
         {/* Logo/Brand */}
         <div className="flex items-center justify-between h-16 px-6 border-b border-neutral-200 flex-shrink-0">
           <div className="flex items-center">
-            <Camera className="w-8 h-8 text-primary-600" />
+            <img src="/picpeak-kamera-transparent.png" alt="Camera" className="w-8 h-8 object-contain" />
             <span className="ml-2 text-xl font-bold text-neutral-900">{t('admin.title')}</span>
           </div>
           <button