feat(portal-shell): add MSW mock layer with production bundle exclusion (P1-5)

MSW v2.7.0 fallback layer covering dashboard/users/exams/grades domains.
NEXT_PUBLIC_MSW=1 enables browser Service Worker + SSR route handler mock
responses without backend. Production build excludes all mock data via
Turbopack resolveAlias redirecting @/mocks to empty stub.

Acceptance: build bundle (client+server) verified clean of mock strings;
typecheck/lint/vitest (231 tests) all pass.

apps/portal-shell/src/lib/apollo-client.ts

@@ -39,6 +39,9 @@ const CLIENT_PROXY_URL = "/api/graphql";
 // 生产环境默认启用（未设置或设置为 true 均启用）
 const APQ_ENABLED = process.env.NEXT_PUBLIC_APOLLO_APQ !== "false";
 
+// MSW 启用时跳过 SSR 查询（P1-5）：浏览器端由 MSW SW 拦截 /api/graphql
+const MSW_ENABLED = process.env.NEXT_PUBLIC_MSW === "1";
+
 /**
  * 创建 Apollo Client 实例。
  *
@@ -54,7 +57,8 @@ export function createApolloClient(
   const isServer = options.serverSide ?? typeof window === "undefined";
 
   const httpLink = new HttpLink({
-    uri: isServer ? SERVER_APOLLO_ROUTER_URL : CLIENT_PROXY_URL,
+    // MSW 启用时（P1-5）：SSR 端也走同域 /api/graphql，由 Route Handler 返回 mock 数据
+    uri: isServer && !MSW_ENABLED ? SERVER_APOLLO_ROUTER_URL : CLIENT_PROXY_URL,
     // 客户端：同域请求，cookie 自动随行；服务端：直连 router 不需要 cookie
     credentials: isServer ? "omit" : "include",
   });