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

apps/lib/shared/widgets/app_input.dart

@@ -1,5 +1,4 @@
 import 'package:flutter/material.dart';
-import '../../core/theme/design_tokens.dart';
 
 class AppInput extends StatelessWidget {
   final String label;
@@ -25,15 +24,16 @@ class AppInput extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
     return Column(
       crossAxisAlignment: CrossAxisAlignment.start,
       children: [
         Text(
           label,
-          style: const TextStyle(
+          style: TextStyle(
             fontSize: 13,
             fontWeight: FontWeight.w500,
-            color: AppColors.slate600,
+            color: colorScheme.onSurfaceVariant,
           ),
         ),
         const SizedBox(height: 6),