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

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

client/test/date_picker_field_test.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:jiu_client/core/theme/themes.dart';
 import 'package:jiu_client/core/utils/date_util.dart';
 import 'package:jiu_client/widgets/date_picker_field.dart';
 
@@ -33,6 +34,7 @@ void main() {
   group('DatePickerField', () {
     testWidgets('渲染可键入框 + 日历图标', (tester) async {
       await tester.pumpWidget(MaterialApp(
+        theme: buildTheme('a'),
         home: Scaffold(
           body: DatePickerField(value: '2026-06-19', onChanged: (_) {}),
         ),
@@ -44,6 +46,7 @@ void main() {
 
     testWidgets('初始值回显到输入框', (tester) async {
       await tester.pumpWidget(MaterialApp(
+        theme: buildTheme('a'),
         home: Scaffold(
           body: DatePickerField(value: '2026-06-19', onChanged: (_) {}),
         ),
@@ -55,6 +58,7 @@ void main() {
     testWidgets('只输年份归一为 yyyy-01-01', (tester) async {
       String? out;
       await tester.pumpWidget(MaterialApp(
+        theme: buildTheme('a'),
         home: Scaffold(
           body: DatePickerField(onChanged: (v) => out = v),
         ),
@@ -66,6 +70,7 @@ void main() {
     testWidgets('年月归一为 yyyy-MM-01', (tester) async {
       String? out;
       await tester.pumpWidget(MaterialApp(
+        theme: buildTheme('a'),
         home: Scaffold(
           body: DatePickerField(onChanged: (v) => out = v),
         ),