refactor(client): widgets 颜色迁移到 context.tokens

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/widgets/date_picker_field.dart

@@ -1,5 +1,5 @@
 import 'package:flutter/material.dart';
-import '../core/theme/app_theme.dart';
+import '../core/theme/context_tokens.dart';
 import '../core/utils/date_util.dart';
 
 /// 可键入日期框 + 日历图标（替代旧的「年/月/日」三下拉）。
@@ -138,8 +138,8 @@ class _DatePickerFieldState extends State<DatePickerField> {
                 const EdgeInsets.symmetric(horizontal: 8, vertical: 8),
             errorText: field.errorText,
             suffixIcon: IconButton(
-              icon: const Icon(Icons.calendar_today,
-                  size: 16, color: AppTheme.textSecondary),
+              icon: Icon(Icons.calendar_today,
+                  size: 16, color: context.tokens.muted),
               padding: EdgeInsets.zero,
               constraints: const BoxConstraints(minWidth: 34, minHeight: 34),
               tooltip: '选择日期',