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/widgets/shared/mini_metric_widget.dart

@@ -29,7 +29,7 @@ class MiniMetricWidget extends StatelessWidget {
           style: AppTypography.badgeText.copyWith(
             color: Theme.of(context).brightness == Brightness.dark 
                 ? AppColors.textSecondaryDark 
-                : AppColors.textSecondaryLight,
+                : AppColors.textSecondary,
           ),
         ),
         const SizedBox(height: 2),
@@ -38,7 +38,7 @@ class MiniMetricWidget extends StatelessWidget {
           style: AppTypography.actionText.copyWith(
             color: valueColor ?? (Theme.of(context).brightness == Brightness.dark 
                 ? AppColors.textPrimaryDark 
-                : AppColors.textPrimaryLight),
+                : AppColors.textPrimary),
           ),
         ),
       ],