refactor: 移除前端 Mock API，新增共享组件，优化认证流程

- 删除 mock_api_client、mock_calendar_service、mock_history_service
- 新增 fixed_length_code_input、link_button、message_composer 共享组件
- 优化登录/注册/密码重置页面使用新组件
- 简化 injection.dart 移除 mock 分支
- 更新 env.dart 配置（BACKEND_URL 替换 API_URL）
- 后端 agentscope 工具和测试更新
- 重构 AGENTS.md 文档结构
- 新增 deploy/ 目录和 protocol 文档

apps/lib/shared/widgets/link_button.dart

@@ -0,0 +1,43 @@
+import 'package:flutter/material.dart';
+
+import '../../core/theme/design_tokens.dart';
+
+class LinkButton extends StatelessWidget {
+  const LinkButton({
+    super.key,
+    required this.text,
+    required this.onTap,
+    this.enabled = true,
+    this.textAlign = TextAlign.center,
+  });
+
+  final String text;
+  final VoidCallback? onTap;
+  final bool enabled;
+  final TextAlign textAlign;
+
+  @override
+  Widget build(BuildContext context) {
+    return SizedBox(
+      height: 44,
+      child: TextButton(
+        onPressed: enabled ? onTap : null,
+        style: TextButton.styleFrom(
+          foregroundColor: enabled ? AppColors.slate500 : AppColors.slate300,
+          padding: const EdgeInsets.symmetric(
+            horizontal: AppSpacing.md,
+            vertical: AppSpacing.sm,
+          ),
+          shape: RoundedRectangleBorder(
+            borderRadius: BorderRadius.circular(AppRadius.sm),
+          ),
+        ),
+        child: Text(
+          text,
+          style: const TextStyle(fontSize: 14, fontWeight: FontWeight.w500),
+          textAlign: textAlign,
+        ),
+      ),
+    );
+  }
+}