Standardize SurClaw ports away from defaults

- Change the API default listen port from 3000 to 3100 and include the Docker frontend origin in default CORS.

- Point Vite's default API proxy, Docker API container port, and Nginx upstream to 3100.

- Keep Docker host ports on 4002 for web, 3002 for API, and 5433 for PostgreSQL.

- Update environment examples and documentation to remove stale localhost:3000 guidance.

AGENTS.md

@@ -24,7 +24,7 @@
 ```bash
 npm install
 npm run dev      # Vite dev server, 0.0.0.0:3001
-npm run server:dev   # build and start NestJS API, 0.0.0.0:3000
+npm run server:dev   # build and start NestJS API, 0.0.0.0:3100
 npm run server:build # tsc -p server/tsconfig.json
 npm run lint     # tsc --noEmit
 npm run test     # vitest run
@@ -287,7 +287,7 @@ npm run test:e2e
 统一前端 API 请求封装：
 
 - 默认请求相对路径 `/api/...`。
-- Vite 开发模式通过 `VITE_API_PROXY_TARGET` 代理 API，默认 `http://localhost:3000`。
+- Vite 开发模式通过 `VITE_API_PROXY_TARGET` 代理 API，默认 `http://localhost:3100`。
 - 请求带 `credentials: 'include'`，用于后端 HttpOnly Session Cookie。
 - 解包后端 `{ data }` 响应，错误时抛出 `ApiError`。