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/models/audit_rule.py

@@ -9,10 +9,11 @@ class AuditRule(Base):
     id = Column(Integer, primary_key=True, autoincrement=True)
     name = Column(String(100), nullable=False, unique=True)
     description = Column(Text, nullable=True)
-    rule_type = Column(String(50), nullable=False)  # syntax / performance / safety / naming
+    rule_type = Column(String(50), nullable=False)  # syntax / performance / safety / naming / DDL / DML
     severity = Column(String(20), default="warning")  # error / warning / info
-    db_type = Column(String(20), default="mysql")  # mysql / postgres / all
+    db_type = Column(String(20), default="mysql")  # mysql / postgres / redis / all
     pattern = Column(Text, nullable=True)  # regex or keyword pattern
+    value = Column(String(255), nullable=True)  # 规则参数值，如 DDLMaxKeyParts=8 → value="8"
     is_enabled = Column(Boolean, default=True)
     message = Column(String(500), nullable=False)  # human-readable message
     created_at = Column(DateTime, server_default=func.now())