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/widgets/info_badge.dart

@@ -13,7 +13,7 @@ class InfoBadge extends StatelessWidget {
   const InfoBadge({
     Key? key,
     required this.text,
-    this.backgroundColor = AppColors.brandGreenLight,
+    this.backgroundColor = AppColors.primaryLight,
     this.textColor = Colors.white,
     this.icon,
   }) : super(key: key);