feat(theme): 重构颜色系统为双主题设计并添加渐变组件

- 引入 "The Kinetic Vault"（深色）和 "The Ethereal Terminal"（浅色）双主题系统
- 重构颜色方案，使用层次化 surface 容器替代边框，遵循无边框设计规则
- 添加渐变预设（CTA、买入/卖出、资产卡片）和渐变按钮组件
- 更新圆角系统，明确按钮、卡片、输入框和标签的圆角规范
- 统一文本样式系统，使用 Space Grotesk（标题）和 Manrope（正文）字体
- 更新现有组件（AssetCard、CoinCard、TradeButton）以遵循新设计规范
- 添加向后兼容的已废弃常量，确保现有代码正常运行

flutter_monisuo/lib/ui/components/trade_button.dart

@@ -1,8 +1,14 @@
 import 'package:flutter/material.dart';
-import 'package:shadcn_ui/shadcn_ui.dart';
 import '../../core/theme/app_color_scheme.dart';
+import '../../core/theme/app_spacing.dart';
 
 /// 交易按钮组件 - 买入/卖出按钮
+///
+/// 设计规则：
+/// - 渐变按钮: 135度渐变
+/// - 圆角: xxl (24px / 1.5rem)
+/// - 买入: 翡翠绿渐变
+/// - 卖出: 红色渐变
 class TradeButton extends StatelessWidget {
   final bool isBuy;
   final String? coinCode;
@@ -39,44 +45,57 @@ class TradeButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final color = isBuy ? AppColorScheme.up : AppColorScheme.down;
-    final text = isBuy ? '买入${coinCode != null ? ' $coinCode' : ''}' : '卖出${coinCode != null ? ' $coinCode' : ''}';
-    final icon = isBuy ? LucideIcons.arrowDownToLine : LucideIcons.arrowUpFromLine;
+    final gradient = isBuy ? AppColorScheme.buyGradient : AppColorScheme.sellGradient;
+    final text = isBuy
+        ? '买入${coinCode != null ? ' $coinCode' : ''}'
+        : '卖出${coinCode != null ? ' $coinCode' : ''}';
 
-    final button = ShadButton(
-      backgroundColor: color,
-      onPressed: isLoading ? null : onPressed,
-      child: Row(
-        mainAxisSize: fullWidth ? MainAxisSize.max : MainAxisSize.min,
-        mainAxisAlignment: MainAxisAlignment.center,
-        children: [
-          if (isLoading)
-            const SizedBox.square(
-              dimension: 16,
-              child: CircularProgressIndicator(
-                strokeWidth: 2,
-                color: Colors.white,
-              ),
-            )
-          else
-            Icon(icon, size: 18, color: Colors.white),
-          const SizedBox(width: 8),
-          Text(
-            text,
-            style: const TextStyle(
-              color: Colors.white,
-              fontSize: 16,
-              fontWeight: FontWeight.w600,
+    return Container(
+      width: fullWidth ? double.infinity : null,
+      height: 48,
+      decoration: BoxDecoration(
+        gradient: gradient,
+        borderRadius: BorderRadius.circular(AppRadius.xxl),
+      ),
+      child: Material(
+        color: Colors.transparent,
+        child: InkWell(
+          onTap: isLoading ? null : onPressed,
+          borderRadius: BorderRadius.circular(AppRadius.xxl),
+          child: Center(
+            child: Row(
+              mainAxisSize: fullWidth ? MainAxisSize.max : MainAxisSize.min,
+              mainAxisAlignment: MainAxisAlignment.center,
+              children: [
+                if (isLoading)
+                  const SizedBox.square(
+                    dimension: 16,
+                    child: CircularProgressIndicator(
+                      strokeWidth: 2,
+                      color: Colors.white,
+                    ),
+                  )
+                else
+                  Icon(
+                    isBuy ? Icons.arrow_downward_rounded : Icons.arrow_upward_rounded,
+                    size: 18,
+                    color: Colors.white,
+                  ),
+                const SizedBox(width: 8),
+                Text(
+                  text,
+                  style: const TextStyle(
+                    color: Colors.white,
+                    fontSize: 16,
+                    fontWeight: FontWeight.w600,
+                  ),
+                ),
+              ],
             ),
           ),
-        ],
+        ),
       ),
     );
-
-    if (fullWidth) {
-      return SizedBox(width: double.infinity, child: button);
-    }
-    return button;
   }
 }
 
@@ -108,7 +127,7 @@ class TradeButtonGroup extends StatelessWidget {
             isLoading: isBuyLoading,
           ),
         ),
-        const SizedBox(width: 12),
+        const SizedBox(width: AppSpacing.sm),
         Expanded(
           child: TradeButton.sell(
             coinCode: coinCode,