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

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

client/lib/widgets/network_retry_button.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
-import '../core/theme/app_theme.dart';
+import '../core/theme/context_tokens.dart';
 import '../providers/connectivity_provider.dart';
 
 /// 离线提示里的「重试」按钮：
@@ -27,7 +27,7 @@ class NetworkRetryButton extends ConsumerWidget {
                 ..hideCurrentSnackBar()
                 ..showSnackBar(SnackBar(
                   content: Text(ok ? '已重新连接服务器' : '仍无法连接服务器，请稍后重试'),
-                  backgroundColor: ok ? AppTheme.success : AppTheme.danger,
+                  backgroundColor: ok ? context.tokens.success : context.tokens.danger,
                   duration: const Duration(seconds: 2),
                   behavior: SnackBarBehavior.floating,
                 ));