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/explore/network_page.dart

@@ -63,7 +63,7 @@ class _NetworkViewState extends State<_NetworkView> {
               color: Theme.of(context).scaffoldBackgroundColor,
               border: Border(
                 bottom: BorderSide(
-                  color: isDark ? AppColors.darkBorder : AppColors.lightBorder,
+                  color: isDark ? AppColors.borderDark : AppColors.border,
                   width: 1,
                 ),
               ),
@@ -75,9 +75,9 @@ class _NetworkViewState extends State<_NetworkView> {
               decoration: InputDecoration(
                 hintText: 'Rechercher des membres, organisations...',
                 hintStyle: AppTypography.subtitleSmall,
-                prefixIcon: const Icon(Icons.search, size: 20, color: AppColors.textSecondaryLight),
+                prefixIcon: const Icon(Icons.search, size: 20, color: AppColors.textSecondary),
                 filled: true,
-                fillColor: isDark ? AppColors.darkSurface : AppColors.lightSurface,
+                fillColor: isDark ? AppColors.surfaceDark : AppColors.surface,
                 contentPadding: const EdgeInsets.symmetric(vertical: 0), // Garder petit
                 border: OutlineInputBorder(
                   borderRadius: BorderRadius.circular(20),
@@ -160,8 +160,8 @@ class _NetworkViewState extends State<_NetworkView> {
                                 },
                                 child: InfoBadge(
                                   text: item.isConnected ? 'Connecté' : 'Suivre',
-                                  backgroundColor: item.isConnected ? AppColors.lightSurface : AppColors.primaryGreen,
-                                  textColor: item.isConnected ? AppColors.textPrimaryLight : Colors.white,
+                                  backgroundColor: item.isConnected ? AppColors.surface : AppColors.primary,
+                                  textColor: item.isConnected ? AppColors.textPrimary : Colors.white,
                                 ),
                               ),
                           ],