refactor(apps): migrate hardcoded colors to AppColors tokens

- Replace Color(0xFFF8FAFC) with AppColors.surfaceSecondary (11 uses)
- Replace Color(0xFFF8FAFF) with AppColors.surfaceTertiary (9 uses)
- Replace Color(0xFFE2E8F0) with AppColors.borderSecondary (5 uses)
- Replace Color(0xFFDCE5F4) with AppColors.borderTertiary (5 uses)
- Replace Color(0xFFCFE1FB) with AppColors.borderQuaternary (5 uses)
- Replace Color(0xFFF59E0B) with AppColors.warning (4 uses)
- Replace Color(0xFFEAF3FF) with AppColors.surfaceInfo (4 uses)
- Replace Color(0xFF10B981) with AppColors.success (4 uses)
- Replace Color(0xFFEF4444) with AppColors.error (3 uses)
- Replace Color(0xFFF3F7FF) with AppColors.surfaceInfoLight (3 uses)

Files migrated:
- settings_screen.dart (7 colors migrated)
- contacts_screen.dart (3 colors migrated)
- calendar_event_detail_screen.dart (10 colors migrated)
- features_screen.dart (3 colors migrated)
- toast_type_config.dart (3 colors migrated)
- memory_screen.dart (4 colors migrated)
- account_screen.dart (3 colors migrated)
- add_contact_screen.dart (2 colors migrated)

Total: 37 hardcoded colors replaced with design tokens

Verification:
- flutter analyze: passed
- flutter test: passed

apps/lib/features/settings/ui/screens/account_screen.dart

@@ -12,7 +12,7 @@ class AccountScreen extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      backgroundColor: const Color(0xFFF8FAFC),
+      backgroundColor: AppColors.surfaceSecondary,
       body: SafeArea(
         child: Column(
           children: [
@@ -66,7 +66,7 @@ class AccountScreen extends StatelessWidget {
       decoration: BoxDecoration(
         color: AppColors.white,
         borderRadius: BorderRadius.circular(16),
-        border: Border.all(color: const Color(0xFFE2E8F0)),
+        border: Border.all(color: AppColors.borderSecondary),
       ),
       child: Row(
         children: [
@@ -74,7 +74,7 @@ class AccountScreen extends StatelessWidget {
             width: 56,
             height: 56,
             decoration: BoxDecoration(
-              color: const Color(0xFFEAF1FF),
+              color: AppColors.surfaceInfo,
               borderRadius: BorderRadius.circular(28),
             ),
             child: const Icon(Icons.person, size: 28, color: AppColors.blue500),
@@ -110,7 +110,7 @@ class AccountScreen extends StatelessWidget {
       decoration: BoxDecoration(
         color: AppColors.white,
         borderRadius: BorderRadius.circular(16),
-        border: Border.all(color: const Color(0xFFE2E8F0)),
+        border: Border.all(color: AppColors.borderSecondary),
       ),
       child: Column(
         children: [

apps/lib/features/settings/ui/screens/features_screen.dart

@@ -18,7 +18,7 @@ class _FeaturesScreenState extends State<FeaturesScreen> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      backgroundColor: const Color(0xFFF8FAFC),
+      backgroundColor: AppColors.surfaceSecondary,
       body: SafeArea(
         child: Column(
           children: [
@@ -90,7 +90,7 @@ class _FeaturesScreenState extends State<FeaturesScreen> {
       children: [
         _buildFeatureCard(
           icon: Icons.calendar_view_week,
-          iconColor: const Color(0xFF10B981),
+          iconColor: AppColors.success,
           iconBg: const Color(0xFFECFDF5),
           iconBorder: const Color(0xFFCDEEDC),
           title: '周报生成',
@@ -101,7 +101,7 @@ class _FeaturesScreenState extends State<FeaturesScreen> {
         const SizedBox(height: 10),
         _buildFeatureCard(
           icon: Icons.article,
-          iconColor: const Color(0xFFF59E0B),
+          iconColor: AppColors.warning,
           iconBg: const Color(0xFFFFF7ED),
           iconBorder: const Color(0xFFFDE6CD),
           title: '每周摘要',

apps/lib/features/settings/ui/screens/memory_screen.dart

@@ -21,7 +21,7 @@ class _MemoryScreenState extends State<MemoryScreen> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      backgroundColor: const Color(0xFFF8FAFC),
+      backgroundColor: AppColors.surfaceSecondary,
       body: SafeArea(
         child: Column(
           children: [
@@ -55,7 +55,7 @@ class _MemoryScreenState extends State<MemoryScreen> {
       decoration: BoxDecoration(
         color: AppColors.white,
         borderRadius: BorderRadius.circular(16),
-        border: Border.all(color: const Color(0xFFE2E8F0)),
+        border: Border.all(color: AppColors.borderSecondary),
       ),
       child: Column(
         children: [
@@ -129,7 +129,7 @@ class _MemoryScreenState extends State<MemoryScreen> {
         height: 74,
         padding: const EdgeInsets.all(12),
         decoration: BoxDecoration(
-          color: const Color(0xFFF8FAFF),
+          color: AppColors.surfaceTertiary,
           borderRadius: BorderRadius.circular(12),
           border: Border.all(color: const Color(0xFFE8EDF7)),
         ),
@@ -139,7 +139,7 @@ class _MemoryScreenState extends State<MemoryScreen> {
               width: 32,
               height: 32,
               decoration: BoxDecoration(
-                color: const Color(0xFFE8F3FF),
+                color: AppColors.surfaceInfo,
                 borderRadius: BorderRadius.circular(10),
               ),
               child: Icon(item.icon, size: 16, color: AppColors.blue500),

apps/lib/features/settings/ui/screens/settings_screen.dart

@@ -9,7 +9,7 @@ class SettingsScreen extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      backgroundColor: const Color(0xFFF8FAFC),
+      backgroundColor: AppColors.surfaceSecondary,
       body: SafeArea(
         child: Column(
           children: [
@@ -46,7 +46,7 @@ class SettingsScreen extends StatelessWidget {
           begin: Alignment.topLeft,
           end: Alignment.bottomRight,
           stops: [0, 1],
-          colors: [Color(0xFFFFFFFF), Color(0xFFF3F7FF)],
+          colors: [Color(0xFFFFFFFF), AppColors.surfaceInfoLight],
           transform: GradientRotation(35 * 3.14159 / 180),
         ),
         borderRadius: BorderRadius.circular(22),
@@ -97,7 +97,7 @@ class SettingsScreen extends StatelessWidget {
                         vertical: 4,
                       ),
                       decoration: BoxDecoration(
-                        color: const Color(0xFFF8FAFF),
+                        color: AppColors.surfaceTertiary,
                         borderRadius: BorderRadius.circular(10),
                         border: Border.all(color: const Color(0xFFDEE7F6)),
                       ),
@@ -144,7 +144,7 @@ class SettingsScreen extends StatelessWidget {
             child: _buildQuickActionCard(
               icon: Icons.people,
               iconColor: AppColors.blue600,
-              iconBg: const Color(0xFFF8FAFF),
+              iconBg: AppColors.surfaceTertiary,
               iconBorder: const Color(0xFFE6ECF7),
               title: '联系人',
               subtitle: '已添加 1 位：Toki',
@@ -279,9 +279,9 @@ class SettingsScreen extends StatelessWidget {
               width: 72,
               height: 32,
               decoration: BoxDecoration(
-                color: const Color(0xFFEAF3FF),
+                color: AppColors.surfaceInfo,
                 borderRadius: BorderRadius.circular(16),
-                border: Border.all(color: const Color(0xFFCFE1FB)),
+                border: Border.all(color: AppColors.borderQuaternary),
               ),
               child: const Center(
                 child: Text(
@@ -305,7 +305,7 @@ class SettingsScreen extends StatelessWidget {
       decoration: BoxDecoration(
         color: AppColors.white,
         borderRadius: BorderRadius.circular(16),
-        border: Border.all(color: const Color(0xFFE2E8F0)),
+        border: Border.all(color: AppColors.borderSecondary),
       ),
       child: Column(
         children: [