refactor(theme): 移除硬编码颜色并统一使用主题系统

- 从多个页面移除对 `app_colors.dart` 的直接引用
- 在资产卡片和主页概览卡片中使用 `AppColorScheme.assetCardGradient` 替代硬编码渐变
- 在注册页面使用 `AppColorScheme` 和 `AppSpacing` 主题常量
- 移除未使用的导入以清理代码

flutter_monisuo/lib/ui/pages/asset/asset_page.dart

@@ -2,7 +2,6 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:shadcn_ui/shadcn_ui.dart';
 import 'package:provider/provider.dart';
-import '../../../core/constants/app_colors.dart';
 import '../../../core/theme/app_color_scheme.dart';
 import '../../../core/theme/app_spacing.dart';
 import '../../../providers/asset_provider.dart';
@@ -85,11 +84,7 @@ class _AssetCard extends StatelessWidget {
       width: double.infinity,
       padding: EdgeInsets.all(AppSpacing.lg),
       decoration: BoxDecoration(
-        gradient: const LinearGradient(
+        gradient: AppColorScheme.assetCardGradient,
-          colors: AppColors.gradientColors,
-          begin: Alignment.topLeft,
-          end: Alignment.bottomRight,
-        ),
         borderRadius: BorderRadius.circular(AppRadius.xl),
       ),
       child: Column(

flutter_monisuo/lib/ui/pages/auth/register_page.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
-import '../../../core/constants/app_colors.dart';
+import '../../../core/theme/app_color_scheme.dart';
+import '../../../core/theme/app_spacing.dart';
 import '../../../providers/auth_provider.dart';
 import '../main/main_page.dart';
 
@@ -31,18 +32,18 @@ class _RegisterPageState extends State<RegisterPage> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      backgroundColor: AppColors.background,
+      backgroundColor: AppColorScheme.darkBackground,
       appBar: AppBar(
         backgroundColor: Colors.transparent,
         elevation: 0,
         leading: IconButton(
-          icon: const Icon(Icons.arrow_back, color: AppColors.textPrimary),
+          icon: const Icon(Icons.arrow_back, color: AppColorScheme.darkOnSurface),
           onPressed: () => Navigator.pop(context),
         ),
       ),
       body: SafeArea(
         child: SingleChildScrollView(
-          padding: const EdgeInsets.all(24),
+          padding: const EdgeInsets.all(AppSpacing.lg),
           child: Form(
             key: _formKey,
             child: Column(
@@ -54,7 +55,7 @@ class _RegisterPageState extends State<RegisterPage> {
                     '\u20BF',
                     style: TextStyle(
                       fontSize: 48,
-                      color: AppColors.primary,
+                      color: AppColorScheme.darkPrimary,
                     ),
                   ),
                 ),
@@ -65,7 +66,7 @@ class _RegisterPageState extends State<RegisterPage> {
                     style: TextStyle(
                       fontSize: 24,
                       fontWeight: FontWeight.bold,
-                      color: AppColors.textPrimary,
+                      color: AppColorScheme.darkOnSurface,
                     ),
                   ),
                 ),
@@ -73,10 +74,10 @@ class _RegisterPageState extends State<RegisterPage> {
                 // 用户名
                 TextFormField(
                   controller: _usernameController,
-                  style: const TextStyle(color: AppColors.textPrimary),
+                  style: const TextStyle(color: AppColorScheme.darkOnSurface),
                   decoration: const InputDecoration(
                     hintText: '请输入账号(4-20位字母数字)',
-                    prefixIcon: Icon(Icons.person_outline, color: AppColors.textSecondary),
+                    prefixIcon: Icon(Icons.person_outline, color: AppColorScheme.darkOnSurfaceVariant),
                   ),
                   validator: (value) {
                     if (value == null || value.isEmpty) {
@@ -96,14 +97,14 @@ class _RegisterPageState extends State<RegisterPage> {
                 TextFormField(
                   controller: _passwordController,
                   obscureText: _obscurePassword,
-                  style: const TextStyle(color: AppColors.textPrimary),
+                  style: const TextStyle(color: AppColorScheme.darkOnSurface),
                   decoration: InputDecoration(
                     hintText: '请输入密码(至少6位)',
-                    prefixIcon: const Icon(Icons.lock_outline, color: AppColors.textSecondary),
+                    prefixIcon: const Icon(Icons.lock_outline, color: AppColorScheme.darkOnSurfaceVariant),
                     suffixIcon: IconButton(
                       icon: Icon(
                         _obscurePassword ? Icons.visibility_off : Icons.visibility,
-                        color: AppColors.textSecondary,
+                        color: AppColorScheme.darkOnSurfaceVariant,
                       ),
                       onPressed: () {
                         setState(() {
@@ -127,14 +128,14 @@ class _RegisterPageState extends State<RegisterPage> {
                 TextFormField(
                   controller: _confirmPasswordController,
                   obscureText: _obscureConfirmPassword,
-                  style: const TextStyle(color: AppColors.textPrimary),
+                  style: const TextStyle(color: AppColorScheme.darkOnSurface),
                   decoration: InputDecoration(
                     hintText: '请再次输入密码',
-                    prefixIcon: const Icon(Icons.lock_outline, color: AppColors.textSecondary),
+                    prefixIcon: const Icon(Icons.lock_outline, color: AppColorScheme.darkOnSurfaceVariant),
                     suffixIcon: IconButton(
                       icon: Icon(
                         _obscureConfirmPassword ? Icons.visibility_off : Icons.visibility,
-                        color: AppColors.textSecondary,
+                        color: AppColorScheme.darkOnSurfaceVariant,
                       ),
                       onPressed: () {
                         setState(() {
@@ -162,7 +163,7 @@ class _RegisterPageState extends State<RegisterPage> {
                       style: ElevatedButton.styleFrom(
                         padding: const EdgeInsets.symmetric(vertical: 16),
                         shape: RoundedRectangleBorder(
-                          borderRadius: BorderRadius.circular(12),
+                          borderRadius: BorderRadius.circular(AppRadius.xxl),
                         ),
                       ),
                       child: auth.isLoading

flutter_monisuo/lib/ui/pages/home/home_page.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:shadcn_ui/shadcn_ui.dart';
 import 'package:provider/provider.dart';
-import '../../../core/constants/app_colors.dart';
+import 'package:flutter_animate/flutter_animate.dart';
 import '../../../core/theme/app_color_scheme.dart';
 import '../../../core/theme/app_spacing.dart';
 import '../../../providers/asset_provider.dart';
@@ -245,11 +245,7 @@ class _AssetOverviewCard extends StatelessWidget {
       width: double.infinity,
       padding: EdgeInsets.all(AppSpacing.lg + AppSpacing.sm),
       decoration: BoxDecoration(
-        gradient: const LinearGradient(
+        gradient: AppColorScheme.assetCardGradient,
-          colors: AppColors.gradientColors,
-          begin: Alignment.topLeft,
-          end: Alignment.bottomRight,
-        ),
         borderRadius: BorderRadius.circular(AppRadius.xl),
       ),
       child: Column(

flutter_monisuo/lib/ui/pages/orders/fund_orders_list.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:shadcn_ui/shadcn_ui.dart';
 import 'package:provider/provider.dart';
-import '../../../core/constants/app_colors.dart';
 import '../../../core/theme/app_spacing.dart';
 import '../../../providers/asset_provider.dart';
 import '../../../data/models/order_models.dart';

flutter_monisuo/lib/ui/pages/orders/orders_page.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:shadcn_ui/shadcn_ui.dart';
 import 'package:provider/provider.dart';
-import '../../../core/constants/app_colors.dart';
 import '../../../core/theme/app_color_scheme.dart';
 import '../../../core/theme/app_spacing.dart';
 import '../../../providers/asset_provider.dart';

flutter_monisuo/lib/ui/pages/trade/trade_page.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:shadcn_ui/shadcn_ui.dart';
 import 'package:provider/provider.dart';
-import '../../../core/constants/app_colors.dart';
 import '../../../core/theme/app_color_scheme.dart';
 import '../../../core/theme/app_spacing.dart';
 import '../../../data/models/coin.dart';