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_card.dart

@@ -89,7 +89,7 @@ class UFCard extends StatelessWidget {
 
     Widget content = Container(
       padding: effectivePadding,
-      decoration: _getDecoration(effectiveBorderRadius),
+      decoration: _getDecoration(effectiveBorderRadius, context),
       child: child,
     );
 
@@ -108,27 +108,31 @@ class UFCard extends StatelessWidget {
     );
   }
 
-  BoxDecoration _getDecoration(double radius) {
+  BoxDecoration _getDecoration(double radius, BuildContext context) {
+    final surfaceColor = Theme.of(context).colorScheme.surface;
+    final isDark = Theme.of(context).brightness == Brightness.dark;
+    final effectiveBorderColor = borderColor ?? (isDark ? AppColors.borderDark : AppColors.border);
+
     switch (style) {
       case UFCardStyle.elevated:
         return BoxDecoration(
-          color: color ?? AppColors.lightSurface,
+          color: color ?? surfaceColor,
           borderRadius: BorderRadius.circular(radius),
         );
 
       case UFCardStyle.outlined:
         return BoxDecoration(
-          color: color ?? AppColors.lightSurface,
+          color: color ?? surfaceColor,
           borderRadius: BorderRadius.circular(radius),
           border: Border.all(
-            color: borderColor ?? AppColors.lightBorder,
+            color: effectiveBorderColor,
             width: borderWidth ?? 1.0,
           ),
         );
 
       case UFCardStyle.filled:
         return BoxDecoration(
-          color: color ?? AppColors.lightSurface,
+          color: color ?? surfaceColor,
           borderRadius: BorderRadius.circular(radius),
         );
     }

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,
                   ),
                 ),
               ),

lib/shared/design_system/components/cards/uf_stat_card.dart

@@ -56,13 +56,13 @@ class UFStatCard 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 effectiveIconBgColor = iconBackgroundColor ??
         effectiveIconColor.withOpacity(0.1);
 
     return Card(
       elevation: SpacingTokens.elevationSm,
-      shadowColor: AppColors.darkBorder.withOpacity(0.1),
+      shadowColor: AppColors.borderDark.withOpacity(0.1),
       shape: RoundedRectangleBorder(
         borderRadius: BorderRadius.circular(SpacingTokens.radiusMd),
       ),
@@ -97,7 +97,7 @@ class UFStatCard extends StatelessWidget {
                     Icon(
                       Icons.arrow_forward_ios,
                       size: 16,
-                      color: isDark ? AppColors.textSecondaryDark : AppColors.textSecondaryLight,
+                      color: isDark ? AppColors.textSecondaryDark : AppColors.textSecondary,
                     ),
                 ],
               ),
@@ -108,7 +108,7 @@ class UFStatCard extends StatelessWidget {
               Text(
                 title,
                 style: AppTypography.badgeText.copyWith(
-                  color: isDark ? AppColors.textSecondaryDark : AppColors.textSecondaryLight,
+                  color: isDark ? AppColors.textSecondaryDark : AppColors.textSecondary,
                 ),
               ),
 
@@ -118,7 +118,7 @@ class UFStatCard extends StatelessWidget {
               Text(
                 value,
                 style: AppTypography.headerSmall.copyWith(
-                  color: isDark ? AppColors.textPrimaryDark : AppColors.textPrimaryLight,
+                  color: isDark ? AppColors.textPrimaryDark : AppColors.textPrimary,
                 ),
               ),
 
@@ -128,7 +128,7 @@ class UFStatCard extends StatelessWidget {
                 Text(
                   subtitle!,
                   style: AppTypography.subtitleSmall.copyWith(
-                    color: isDark ? AppColors.textSecondaryDark : AppColors.textSecondaryLight,
+                    color: isDark ? AppColors.textSecondaryDark : AppColors.textSecondary,
                   ),
                 ),
               ],