feat: 添加视觉设计语言系统并重构认证页面UI

- 新增 visual_design_language.md 设计规范文档
- 新增 auth 设计 tokens (authBackground, authCard, authInput, feedback 系列等)
- 重构登录/注册/验证码/重置密码页面为新设计系统
- 新增 AuthHeroHeader, AuthSurfaceCard, AuthSection, AuthField, PasswordField 组件
- 重构 AppBanner 和 Toast 支持多类型配置 (info/success/warning/error)
- 后端 AgentScope: 重整 schemas/prompts/tools 作用域, 新增协议文档
- 更新 AGENTS.md 集成视觉设计语言约束

apps/lib/shared/widgets/banner/app_banner.dart

@@ -7,12 +7,14 @@ class AppBanner extends StatelessWidget {
   final String message;
   final ToastType type;
   final bool visible;
+  final String? title;
 
   const AppBanner({
     super.key,
     required this.message,
     this.type = ToastType.warning,
     this.visible = true,
+    this.title,
   });
 
   @override
@@ -23,19 +25,47 @@ class AppBanner extends StatelessWidget {
 
     return Container(
       width: double.infinity,
-      padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 10),
+      padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 12),
       decoration: BoxDecoration(
-        color: config.backgroundColor,
-        borderRadius: BorderRadius.circular(AppRadius.sm),
+        color: config.surfaceColor,
+        borderRadius: BorderRadius.circular(AppRadius.md),
+        border: Border.all(color: config.borderColor),
       ),
       child: Row(
+        crossAxisAlignment: CrossAxisAlignment.start,
         children: [
-          Icon(config.icon, size: 16, color: config.iconColor),
+          Container(
+            width: 28,
+            height: 28,
+            decoration: BoxDecoration(
+              color: config.iconColor.withValues(alpha: 0.12),
+              borderRadius: BorderRadius.circular(AppRadius.full),
+            ),
+            child: Icon(config.icon, size: 16, color: config.iconColor),
+          ),
           const SizedBox(width: 8),
           Expanded(
-            child: Text(
-              message,
-              style: TextStyle(fontSize: 13, color: config.textColor),
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text(
+                  title ?? config.label,
+                  style: TextStyle(
+                    fontSize: 12,
+                    fontWeight: FontWeight.w700,
+                    color: config.textColor,
+                  ),
+                ),
+                const SizedBox(height: 2),
+                Text(
+                  message,
+                  style: TextStyle(
+                    fontSize: 13,
+                    height: 1.35,
+                    color: config.textColor,
+                  ),
+                ),
+              ],
             ),
           ),
         ],