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/shared/design_system/components/cards/uf_info_card.dart

@@ -50,13 +50,13 @@ class UFInfoCard extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final isDark = Theme.of(context).brightness == Brightness.dark;
-    final effectiveIconColor = iconColor ?? AppColors.primaryGreen;
+    final effectiveIconColor = iconColor ?? AppColors.primary;
     final effectivePadding = padding ?? const EdgeInsets.all(SpacingTokens.lg);
 
     return Container(
       padding: effectivePadding,
       decoration: BoxDecoration(
-        color: isDark ? AppColors.darkSurface : Colors.white,
+        color: isDark ? AppColors.surfaceDark : Colors.white,
         borderRadius: BorderRadius.circular(SpacingTokens.radiusMd),
       ),
       child: Column(
@@ -71,7 +71,7 @@ class UFInfoCard extends StatelessWidget {
                 child: Text(
                   title,
                   style: AppTypography.headerSmall.copyWith(
-                    color: isDark ? AppColors.textPrimaryDark : AppColors.textPrimaryLight,
+                    color: isDark ? AppColors.textPrimaryDark : AppColors.textPrimary,
                   ),
                 ),
               ),