Fix public page layouts and avatar display

🎨 Layout improvements:
- Add full implementations for timeline, masonry, and magazine layouts
- Replace layout stubs with proper React components matching dashboard
- Add timeline with alternating left/right positioning and central line
- Implement masonry layout with dynamic column sizing
- Create magazine layout with featured first item and image previews

🐛 Avatar & URL fixes:
- Fix avatar URL protocol (http → https) in normalize_file_url
- Add http://links.shareon.kr to internal URLs replacement list
- Update get_backend_url to use HTTPS and proper domain from env vars
- Fix CustomizationPanel API URL consistency in DashboardClient

✨ Visual enhancements:
- Proper hover states and transitions for all layout types
- Timeline dots with theme color coordination
- Magazine layout with responsive image handling
- Masonry cards with dynamic content sizing
- Consistent group/link styling across all layouts

🔧 Technical:
- Environment-driven URL generation for production
- Consistent API endpoint usage across components
- Better responsive design for mobile devices
- Improved accessibility with proper alt text and ARIA labels

frontend/linktree-frontend/src/app/(protected)/dashboard/DashboardClient.tsx

@@ -210,7 +210,7 @@ export default function DashboardClient() {
       fetch('/api/auth/user', { headers: { Authorization: `Bearer ${token}` } }),
       fetch('/api/groups', { headers: { Authorization: `Bearer ${token}` } }),
       fetch('/api/links', { headers: { Authorization: `Bearer ${token}` } }),
-      fetch('/api/customization/settings', { headers: { Authorization: `Bearer ${token}` } }),
+      fetch('/api/customization/settings/', { headers: { Authorization: `Bearer ${token}` } }),
     ])
       .then(async ([uRes, gRes, lRes, dRes]) => {
         if (!uRes.ok) throw new Error('Не удалось получить профиль')