refactor(apps): 主题系统迁移至 ColorScheme + 扩展架构并支持 Dark Mode

apps/lib/shared/widgets/phone_prefix_selector.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import '../../core/theme/design_tokens.dart';
 
 class PhonePrefixSelector extends StatelessWidget {
   const PhonePrefixSelector({
@@ -15,8 +14,9 @@ class PhonePrefixSelector extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
     return Padding(
-      padding: const EdgeInsets.only(left: AppSpacing.md, right: AppSpacing.sm),
+      padding: const EdgeInsets.only(left: 12, right: 8),
       child: PopupMenuButton<String>(
         onSelected: onChanged,
         itemBuilder: (context) => items
@@ -24,26 +24,24 @@ class PhonePrefixSelector extends StatelessWidget {
               (item) => PopupMenuItem<String>(value: item, child: Text(item)),
             )
             .toList(growable: false),
-        color: AppColors.white,
-        shape: RoundedRectangleBorder(
-          borderRadius: BorderRadius.circular(AppRadius.md),
-        ),
+        color: colorScheme.surface,
+        shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(12)),
         child: Row(
           mainAxisSize: MainAxisSize.min,
           children: [
             Text(
               value,
-              style: const TextStyle(
+              style: TextStyle(
                 fontSize: 15,
                 fontWeight: FontWeight.w500,
-                color: AppColors.slate700,
+                color: colorScheme.onSurface,
               ),
             ),
-            const SizedBox(width: AppSpacing.xs),
-            const Icon(
+            const SizedBox(width: 4),
+            Icon(
               Icons.arrow_drop_down,
               size: 18,
-              color: AppColors.slate500,
+              color: colorScheme.onSurfaceVariant,
             ),
           ],
         ),