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/trade/components/confirm_dialog.dart

@@ -49,14 +49,14 @@ class ConfirmDialog extends StatelessWidget {
               ),
             ),
             SizedBox(height: AppSpacing.lg),
-            _dialogRow('交易对', '$coinCode/USDT', colorScheme),
+            _dialogRow(context, '交易对', '$coinCode/USDT', colorScheme),
             SizedBox(height: AppSpacing.sm),
-            _dialogRow('委托价格', '$price USDT', colorScheme),
+            _dialogRow(context, '委托价格', '$price USDT', colorScheme),
             SizedBox(height: AppSpacing.sm),
-            _dialogRow('交易金额', '$amount USDT', colorScheme,
+            _dialogRow(context, '交易金额', '$amount USDT', colorScheme,
                 valueColor: actionColor),
             SizedBox(height: AppSpacing.sm),
-            _dialogRow('交易数量', '$quantity $coinCode', colorScheme),
+            _dialogRow(context, '交易数量', '$quantity $coinCode', colorScheme),
             SizedBox(height: AppSpacing.lg),
             Row(
               children: [
@@ -87,7 +87,7 @@ class ConfirmDialog extends StatelessWidget {
     );
   }
 
-  Widget _dialogRow(String label, String value, ColorScheme colorScheme,
+  Widget _dialogRow(BuildContext context, String label, String value, ColorScheme colorScheme,
       {Color? valueColor}) {
     return Row(
       mainAxisAlignment: MainAxisAlignment.spaceBetween,

flutter_monisuo/lib/ui/pages/trade/components/trade_form_card.dart

@@ -172,13 +172,13 @@ class TradeFormCard extends StatelessWidget {
           // 设计稿：gap:8，圆角sm，bg-tertiary，高32
           Row(
             children: [
-              _buildPctButton('25%', 0.25, colorScheme),
+              _buildPctButton(context, '25%', 0.25, colorScheme),
               const SizedBox(width: AppSpacing.sm),
-              _buildPctButton('50%', 0.5, colorScheme),
+              _buildPctButton(context, '50%', 0.5, colorScheme),
               const SizedBox(width: AppSpacing.sm),
-              _buildPctButton('75%', 0.75, colorScheme),
+              _buildPctButton(context, '75%', 0.75, colorScheme),
               const SizedBox(width: AppSpacing.sm),
-              _buildPctButton('100%', 1.0, colorScheme),
+              _buildPctButton(context, '100%', 1.0, colorScheme),
             ],
           ),
           const SizedBox(height: AppSpacing.md + AppSpacing.sm),
@@ -203,7 +203,7 @@ class TradeFormCard extends StatelessWidget {
   }
 
   /// 百分比按钮 - 设计稿：圆角sm，bg-tertiary，高32
-  Widget _buildPctButton(String label, double pct, ColorScheme colorScheme) {
+  Widget _buildPctButton(BuildContext context, String label, double pct, ColorScheme colorScheme) {
     return Expanded(
       child: GestureDetector(
         onTap: () => onFillPercent(pct),