feat: 审核规则模版+设置页面整合+去掉角色切换demo

后端:
- AuditRule 新增 value 字段, rule_type 扩展 DDL/DML
- MySQL/PG/Redis 预设规则种子接口 POST /audit-rules/seed/{db_type}
- 公告管理 CRUD (announcements)
- 消息推送 CRUD+测试 (notifications: 钉钉/飞书/邮件)
- LDAP 配置 CRUD+测试连接 (ldap-config)
- 164 tests passing (+31 新增)

前端:
- AuditRulesPage 重写: DB类型Tab+DDL/DML分组+参数编辑
- SettingsPage: 系统设置主页(审核规则/公告/推送/LDAP)
- NotificationPage: 钉钉/飞书/SMTP配置
- LdapConfigPage: LDAP设置+测试连接
- AnnouncementPage: 公告Markdown编辑
- 去掉左下角角色切换demo
- 侧边栏合并为: 系统设置(含审核规则+公告+推送+LDAP)

backend/app/schemas/notification.py

@@ -0,0 +1,30 @@
+from datetime import datetime
+from typing import Optional, Dict, Any
+from pydantic import BaseModel, Field
+
+
+class NotificationChannelCreate(BaseModel):
+    name: str = Field(..., min_length=1, max_length=100)
+    channel_type: str = Field(..., pattern=r"^(dingtalk|webhook_feishu|email)$")
+    config: Dict[str, Any]
+    is_enabled: bool = True
+
+
+class NotificationChannelUpdate(BaseModel):
+    name: Optional[str] = Field(default=None, min_length=1, max_length=100)
+    channel_type: Optional[str] = Field(default=None, pattern=r"^(dingtalk|webhook_feishu|email)$")
+    config: Optional[Dict[str, Any]] = None
+    is_enabled: Optional[bool] = None
+
+
+class NotificationChannelResponse(BaseModel):
+    id: int
+    name: str
+    channel_type: str
+    config: Dict[str, Any]  # passwords masked in endpoint
+    is_enabled: bool
+    created_at: datetime
+    updated_at: datetime
+
+    class Config:
+        from_attributes = True