feat(shared): legacy presentation/ + shared design system + widgets

- lib/presentation : pages legacy (explore/network, notifications) avec BLoC
- lib/shared/design_system : UnionFlow Design System v2 (tokens, components)
  + MD3 tokens + module_colors par feature
- lib/shared/widgets : widgets transversaux (core_card, core_shimmer,
  error_widget, loading_widget, powered_by_lions_dev, etc.)
- lib/shared/constants + utils

lib/presentation/notifications/notification_page.dart

@@ -116,7 +116,7 @@ class _NotificationView extends StatelessWidget {
               itemCount: state.items.length,
               itemBuilder: (context, index) {
                 final item = state.items[index];
-                final unreadColor = isDark ? const Color(0xFF1B2E26) : const Color(0xFFE8F5E9); 
+                final unreadColor = isDark ? const Color(0xFF1A1F2E) : const Color(0xFFEFF6FF); 
 
                 return InkWell(
                   onTap: () {
@@ -136,8 +136,8 @@ class _NotificationView extends StatelessWidget {
                           Icon(
                             item.category == 'finance' ? Icons.payment : Icons.event,
                             color: item.isRead 
-                                ? (isDark ? AppColors.textSecondaryDark : AppColors.textSecondaryLight)
-                                : AppColors.primaryGreen,
+                                ? (isDark ? AppColors.textSecondaryDark : AppColors.textSecondary)
+                                : AppColors.primary,
                             size: 20,
                           ),
                           const SizedBox(width: 12),