feat(mcp): 设置 → MCP 子页 + 策略 API + 官网/文档接入

借鉴 DBX：安装检测（Node/npm/包/Go 二进制）、只读与 allow_dangerous、
连接白名单、多客户端配置片段；GET/PUT /api/ai/mcp-policy、/mcp-install；
文档 /docs/mcp 与落地页 AI/MCP 块；对照 docs/16 勾选设置项、列仍未完清单。

src/api.ts

@@ -684,14 +684,64 @@ export type McpStatus = {
   mode: string;
   whitelistCount: number;
   writesEnabled: boolean;
+  allowDangerous?: boolean;
   active: boolean;
   recent?: { time: string; tool: string; ok: boolean; summary?: string; error?: string; source?: string }[];
+  policyPath?: string;
+};
+
+export type McpPolicy = {
+  allowed_connection_ids: string[];
+  mode: "read_only" | "read_write" | string;
+  allow_dangerous?: boolean;
+  default_limit?: number;
+  max_limit?: number;
+};
+
+export type McpInstallInfo = {
+  status: "ready" | "partial" | "not_installed" | string;
+  installed: boolean;
+  currentVersion?: string;
+  latestVersion?: string;
+  nodeVersion?: string;
+  npmAvailable: boolean;
+  npmVersion?: string;
+  npmPackageInstalled: boolean;
+  npmPackageVersion?: string;
+  goBinaryFound: boolean;
+  goBinaryPath?: string;
+  installCommand: string;
+  npxCommand?: string;
+  policyPath?: string;
+  hint?: string;
 };
 
 export async function getMcpStatus(signal?: AbortSignal) {
   return get<McpStatus>("/api/ai/mcp-status", signal);
 }
 
+export async function getMcpPolicy(signal?: AbortSignal) {
+  return get<{ policy: McpPolicy; path?: string }>("/api/ai/mcp-policy", signal);
+}
+
+export async function saveMcpPolicy(policy: McpPolicy, signal?: AbortSignal) {
+  const res = await fetch(`${API}/api/ai/mcp-policy`, {
+    method: "PUT",
+    headers: { "Content-Type": "application/json", ...authHeaders() },
+    body: JSON.stringify(policy),
+    signal,
+  });
+  const data = await res.json().catch(() => ({}));
+  if (!res.ok) {
+    throw new Error((data as { error?: string }).error || res.statusText || "request failed");
+  }
+  return data as { ok: boolean; policy: McpPolicy; path?: string };
+}
+
+export async function getMcpInstall(signal?: AbortSignal) {
+  return get<McpInstallInfo>("/api/ai/mcp-install", signal);
+}
+
 export async function confirmAiAgentWrite(payload: {
   connectionId: string;
   sql?: string;