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/dashboard_theme_manager.dart

@@ -1,21 +1,22 @@
 import 'package:flutter/material.dart';
+import 'tokens/color_tokens.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
 /// Gestionnaire de thèmes personnalisables pour le Dashboard
 class DashboardThemeManager {
   static const String _themeKey = 'dashboard_theme';
-  static DashboardThemeData _currentTheme = DashboardThemeData.royalTeal();
+  static DashboardThemeData _currentTheme = DashboardThemeData.unionFlow();
   static SharedPreferences? _prefs;
-  
+
   /// Initialise le gestionnaire de thèmes
   static Future<void> initialize() async {
     _prefs = await SharedPreferences.getInstance();
     await _loadSavedTheme();
   }
-  
+
   /// Charge le thème sauvegardé
   static Future<void> _loadSavedTheme() async {
-    final themeName = _prefs?.getString(_themeKey) ?? 'royalTeal';
+    final themeName = _prefs?.getString(_themeKey) ?? 'unionFlow';
     _currentTheme = _getThemeByName(themeName);
   }
   
@@ -31,6 +32,8 @@ class DashboardThemeManager {
   /// Obtient un thème par son nom
   static DashboardThemeData _getThemeByName(String name) {
     switch (name) {
+      case 'unionFlow':
+        return DashboardThemeData.unionFlow();
       case 'royalTeal':
         return DashboardThemeData.royalTeal();
       case 'oceanBlue':
@@ -44,12 +47,13 @@ class DashboardThemeManager {
       case 'darkMode':
         return DashboardThemeData.darkMode();
       default:
-        return DashboardThemeData.royalTeal();
+        return DashboardThemeData.unionFlow();
     }
   }
-  
+
   /// Obtient la liste des thèmes disponibles
   static List<ThemeOption> get availableThemes => [
+    ThemeOption('unionFlow', 'UnionFlow (défaut)', DashboardThemeData.unionFlow()),
     ThemeOption('royalTeal', 'Bleu Roi & Pétrole', DashboardThemeData.royalTeal()),
     ThemeOption('oceanBlue', 'Bleu Océan', DashboardThemeData.oceanBlue()),
     ThemeOption('forestGreen', 'Vert Forêt', DashboardThemeData.forestGreen()),
@@ -108,7 +112,29 @@ class DashboardThemeData {
     this.isDark = false,
   });
   
-  /// Thème Bleu Roi & Pétrole (par défaut)
+  /// Thème UnionFlow officiel — Bleu #297FFF → Violet #7616E8 (logo signature)
+  factory DashboardThemeData.unionFlow() {
+    return const DashboardThemeData(
+      name: 'UnionFlow',
+      primaryColor: Color(0xFF297FFF),
+      secondaryColor: Color(0xFF7616E8),
+      primaryLight: Color(0xFF69B7FF),
+      primaryDark: Color(0xFF2170E7),
+      secondaryLight: Color(0xFF9B59F0),
+      secondaryDark: Color(0xFF5B0FBA),
+      backgroundColor: Color(0xFFF5F8FF),
+      surfaceColor: Color(0xFFFFFFFF),
+      cardColor: Color(0xFFFFFFFF),
+      textPrimary: Color(0xFF111827),
+      textSecondary: Color(0xFF6B7280),
+      success: Color(0xFF22C55E),
+      warning: Color(0xFFF59E0B),
+      error: Color(0xFFEF4444),
+      info: Color(0xFF297FFF),
+    );
+  }
+
+  /// Thème Bleu Roi & Pétrole
   factory DashboardThemeData.royalTeal() {
     return const DashboardThemeData(
       name: 'Bleu Roi & Pétrole',
@@ -123,7 +149,7 @@ class DashboardThemeData {
       cardColor: Color(0xFFFFFFFF),
       textPrimary: Color(0xFF111827),
       textSecondary: Color(0xFF6B7280),
-      success: Color(0xFF10B981),
+      success: ColorTokens.successLight,
       warning: Color(0xFFF59E0B),
       error: Color(0xFFEF4444),
       info: Color(0xFF3B82F6),
@@ -158,7 +184,7 @@ class DashboardThemeData {
       name: 'Vert Forêt',
       primaryColor: Color(0xFF059669),
       secondaryColor: Color(0xFF047857),
-      primaryLight: Color(0xFF10B981),
+      primaryLight: ColorTokens.successLight,
       primaryDark: Color(0xFF065F46),
       secondaryLight: Color(0xFF059669),
       secondaryDark: Color(0xFF064E3B),
@@ -167,7 +193,7 @@ class DashboardThemeData {
       cardColor: Color(0xFFFFFFFF),
       textPrimary: Color(0xFF064E3B),
       textSecondary: Color(0xFF6B7280),
-      success: Color(0xFF10B981),
+      success: ColorTokens.successLight,
       warning: Color(0xFFF59E0B),
       error: Color(0xFFEF4444),
       info: Color(0xFF3B82F6),
@@ -227,7 +253,7 @@ class DashboardThemeData {
       primaryLight: Color(0xFF93C5FD),
       primaryDark: Color(0xFF3B82F6),
       secondaryLight: Color(0xFF6EE7B7),
-      secondaryDark: Color(0xFF10B981),
+      secondaryDark: ColorTokens.successLight,
       backgroundColor: Color(0xFF111827),
       surfaceColor: Color(0xFF1F2937),
       cardColor: Color(0xFF374151),