refactor: 清理SQL审计全栈死代码 (删除孤立组件+handler+model+路由+mock+API定义, 共-1278行)

SQL审计菜单此前已从侧边栏移除，但死代码残留(违反step5清理清单):
- 删除 frontend/components/audit/SQLAuditManager.tsx (629行, 无任何外部引用)
- 删除 backend/handlers/sql_audit.go (435行) + backend/models/sql_audit.go (64行)
- 移除 routes.go 中13条SQL审计路由 (API不再暴露, 返回404)
- 移除 database.go AutoMigrate 中2个SQL审计表
- 移除 api.ts sqlAuditApi 对象 (37行)
- 移除 mocks SQL审计mock数据 (90行) + barrel引用

frontend/src/services/api.ts

@@ -527,43 +527,6 @@ export const auditApi = {
   },
 };
 
-// ==================== SQL 审计 API ====================
-export const sqlAuditApi = {
-  getRecords: async (params?: Record<string, string>) => {
-    return http.get<ListResponse>('/sql-audit/records', params);
-  },
-  getRules: async () => {
-    return http.get<ListResponse>('/sql-audit/rules');
-  },
-  analyzeSQL: async (data: { sql: string; database_name?: string; application?: string }) => {
-    return http.post('/sql-audit/analyze', data);
-  },
-  approve: async (id: string | number) => {
-    return http.post(`/sql-audit/records/${id}/approve`);
-  },
-  reject: async (id: string | number) => {
-    return http.post(`/sql-audit/records/${id}/reject`);
-  },
-  execute: async (id: string | number) => {
-    return http.post(`/sql-audit/records/${id}/execute`);
-  },
-  deleteRecord: async (id: string | number) => {
-    return http.delete(`/sql-audit/records/${id}`);
-  },
-  createRule: async (data: any) => {
-    return http.post('/sql-audit/rules', data);
-  },
-  updateRule: async (id: string | number, data: any) => {
-    return http.put(`/sql-audit/rules/${id}`, data);
-  },
-  deleteRule: async (id: string | number) => {
-    return http.delete(`/sql-audit/rules/${id}`);
-  },
-  toggleRule: async (ruleId: string | number) => {
-    return http.post(`/sql-audit/rules/${ruleId}/toggle`);
-  },
-};
-
 // ==================== Ansible 自动化 API ====================
 export const ansibleApi = {
   // Playbook 管理