fix(dev): 本地 API 默认端口改为 3100 避开 Windows 保留段

Hyper-V 常保留 2960-3059，3000 会 EACCES；ensure-port-free 与 Vite 代理从 apps/api/.env 读取 PORT

scripts/ensure-port-free.mjs

@@ -1,6 +1,7 @@
 import { execSync } from 'node:child_process';
+import { resolveApiDevPort } from './dev-api-target.mjs';
 
-const port = process.argv[2] ?? '3000';
+const port = process.argv[2] ?? resolveApiDevPort();
 
 function killWindows(portNum) {
   let out = '';