feat(server): 单域托管 client/dist 与 SPA 回退（E12）

- 新增 SERVE_CLIENT_DIST/CLIENT_DIST_DIR 配置
- 开启后注册 @fastify/static 并对非 /api GET(html) 回退 index.html
- docker-compose.yml 与 README 补充用法

server/src/app.js

@@ -9,6 +9,7 @@ const cookie = require("@fastify/cookie");
 const multipart = require("@fastify/multipart");
 const helmet = require("@fastify/helmet");
 const rateLimit = require("@fastify/rate-limit");
+const staticPlugin = require("@fastify/static");
 
 const { getConfig } = require("./config");
 const authPlugin = require("./plugins/auth");
@@ -95,11 +96,29 @@ async function buildApp() {
     },
   });
 
+  if (config.serveClientDist) {
+    await app.register(staticPlugin, {
+      root: config.clientDistDir,
+    });
+    app.log.info({ dir: config.clientDistDir }, "Client dist static serving enabled");
+  }
+
   app.addHook("onRequest", async (request, reply) => {
     reply.header("x-request-id", request.id);
   });
 
-  app.setNotFoundHandler(async () => {
+  app.setNotFoundHandler(async (request, reply) => {
+    if (
+      config.serveClientDist &&
+      request.method === "GET" &&
+      !request.url.startsWith("/api") &&
+      typeof request.headers.accept === "string" &&
+      request.headers.accept.includes("text/html") &&
+      typeof reply.sendFile === "function"
+    ) {
+      return reply.type("text/html").sendFile("index.html");
+    }
+
     throw new AppError({
       code: "SYS_404",
       message: "Not Found",