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/feed/unified_feed_page.dart

@@ -96,7 +96,7 @@ class _UnifiedFeedViewState extends State<_UnifiedFeedView> {
           ),
         ),
         body: RefreshIndicator(
-        color: AppColors.primaryGreen,
+        color: AppColors.primary,
         backgroundColor: Theme.of(context).scaffoldBackgroundColor,
         onRefresh: () async {
           context.read<UnifiedFeedBloc>().add(const LoadFeedRequested(isRefresh: true));
@@ -189,8 +189,8 @@ class _UnifiedFeedViewState extends State<_UnifiedFeedView> {
                           const SizedBox(width: 6),
                           InfoBadge(
                             text: item.type.name.toUpperCase(),
-                            backgroundColor: AppColors.primaryGreen.withOpacity(0.1),
-                            textColor: AppColors.primaryGreen,
+                            backgroundColor: AppColors.primary.withOpacity(0.1),
+                            textColor: AppColors.primary,
                           ),
                         ]
                       ],
@@ -206,7 +206,7 @@ class _UnifiedFeedViewState extends State<_UnifiedFeedView> {
                   size: 16,
                   color: Theme.of(context).brightness == Brightness.dark 
                       ? AppColors.textSecondaryDark 
-                      : AppColors.textSecondaryLight,
+                      : AppColors.textSecondary,
                 ),
                 onPressed: () => _showPostOptionsMenu(context, item),
               )