fix(theme): 修复亮色模式绿色对比度不足问题

- 添加主题感知颜色函数: getUpColor/getUpBackgroundColor
- app_color_scheme: 新增 getBuyGradient/getEmeraldGradient
- asset_card: emeraldGradient 支持主题切换
- neon_glow: 按钮颜色主题感知
- home_page: 涨跌颜色动态适配
- asset_page: 资产涨跌颜色适配
- trade_page: 交易涨跌颜色适配
- mine_page: 我的页面颜色适配

修复: 亮色模式下绿色 (#00a878) 与浅色背景对比度不足
效果: 亮色模式使用深绿色，深色模式使用亮绿色

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

@@ -406,6 +406,7 @@ class _HoldingItem extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final colorScheme = Theme.of(context).colorScheme;
+    final isDark = Theme.of(context).brightness == Brightness.dark;
 
     return Padding(
       padding: EdgeInsets.symmetric(vertical: AppSpacing.sm),
@@ -464,7 +465,7 @@ class _HoldingItem extends StatelessWidget {
               Text(
                 holding.formattedProfitRate,
                 style: TextStyle(
-                  color: holding.isProfit ? AppColorScheme.up : AppColorScheme.down,
+                  color: holding.isProfit ? AppColorScheme.getUpColor(isDark) : AppColorScheme.down,
                   fontSize: 12,
                   fontWeight: FontWeight.w600,
                 ),
@@ -598,6 +599,7 @@ void _showDepositResultDialog(BuildContext context, Map<String, dynamic> data) {
   final walletAddress = data['walletAddress'] as String? ?? '';
   final walletNetwork = data['walletNetwork'] as String? ?? 'TRC20';
   final colorScheme = Theme.of(context).colorScheme;
+  final isDark = Theme.of(context).brightness == Brightness.dark;
 
   showShadDialog(
     context: context,
@@ -614,7 +616,7 @@ void _showDepositResultDialog(BuildContext context, Map<String, dynamic> data) {
               children: [
                 NeonIcon(
                   icon: Icons.check_circle,
-                  color: AppColorScheme.up,
+                  color: AppColorScheme.getUpColor(isDark),
                   size: 24,
                 ),
                 SizedBox(width: AppSpacing.sm),