feat(theme): migrate to new theme system with static color methods

- Convert instance methods to static methods in AppColorScheme for
  getChangeColor and getChangeBackgroundColor
- Update main.dart to use ShadThemeData with AppColorScheme color
  schemes instead of createLight/DarkShadTheme functions
- Add app_theme.dart import to main.dart
- Refactor asset_card.dart and coin_card.dart to call static methods
  via AppColorScheme class
- Add app_spacing.dart import to action_buttons_row.dart
- Replace SizedBox with proper spacing constants in action buttons row

flutter_monisuo/lib/ui/pages/mine/components/logout_button.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:google_fonts/google_fonts.dart';
 import '../../../../core/theme/app_color_scheme.dart';
 import '../../../../core/theme/app_spacing.dart';
+import '../../../../core/theme/app_theme.dart';
 
 /// 退出登录按钮
 class LogoutButton extends StatelessWidget {

flutter_monisuo/lib/ui/pages/mine/components/profile_card.dart

@@ -23,7 +23,7 @@ class ProfileCard extends StatelessWidget {
             : colorScheme.surfaceContainerHigh,
         borderRadius: BorderRadius.circular(AppRadius.lg),
         border: Border.all(
-          color: colorScheme.outlineVariant.withOpacity(0.15),
+          color: colorScheme.outlineVariant.withValues(alpha: 0.15),
         ),
       ),
       child: Row(
@@ -47,10 +47,8 @@ class ProfileCard extends StatelessWidget {
                 const SizedBox(height: 4),
                 Text(
                   '普通用户',
-                  style: GoogleFonts.inter(
-                    fontSize: 10,
+                  style: AppTextStyles.bodyMedium(context).copyWith(
                     fontWeight: FontWeight.normal,
-                    color: colorScheme.onSurfaceVariant,
                   ),
                 ),
               ],