chore(deploy): add same-host staging stack next to production

dev deploys to /opt/dukang-staging (819x, *-test domains); main deploys to production. Staging uses full Mock with shared WeChat app ids.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/dukang-api/src/load-env.ts

@@ -5,19 +5,33 @@ import { resolve } from 'path';
 /**
  * 环境变量加载策略（后加载的文件覆盖先前的同名键）：
  *
- * - 本地开发：仅 `.env` + `.env.local`
- *   `.env.development` 仅作参考模板，不自动加载
+ * - local：`.env` + `.env.local`
+ * - staging：`.env.staging` + `.env.staging.local`（同机测试栈，APP_ENV=staging）
+ * - production：`.env.production` + `.env.production.local`
  *
- * - 服务器（NODE_ENV=production）：仅 `.env.production` + `.env.production.local`
- *   不使用 `.env`，避免与本地开发配置混淆
+ * 判定：优先 `APP_ENV`；未设置时 `NODE_ENV=production` → production，否则 local。
+ * staging 在 PM2 中仍设 `NODE_ENV=production`（构建产物），靠 `APP_ENV=staging` 区分。
  */
 const apiRoot = resolve(__dirname, '..');
 const nodeEnv = process.env.NODE_ENV ?? 'development';
-const isProduction = nodeEnv === 'production';
 
-const layers = isProduction
-  ? [resolve(apiRoot, '.env.production'), resolve(apiRoot, '.env.production.local')]
-  : [resolve(apiRoot, '.env'), resolve(apiRoot, '.env.local')];
+function resolveAppEnv(): 'local' | 'staging' | 'production' {
+  const raw = (process.env.APP_ENV ?? '').trim().toLowerCase();
+  if (raw === 'staging' || raw === 'stage' || raw === 'test') return 'staging';
+  if (raw === 'production' || raw === 'prod') return 'production';
+  if (raw === 'local' || raw === 'development' || raw === 'dev') return 'local';
+  if (nodeEnv === 'production') return 'production';
+  return 'local';
+}
+
+const appEnv = resolveAppEnv();
+
+const layers =
+  appEnv === 'staging'
+    ? [resolve(apiRoot, '.env.staging'), resolve(apiRoot, '.env.staging.local')]
+    : appEnv === 'production'
+      ? [resolve(apiRoot, '.env.production'), resolve(apiRoot, '.env.production.local')]
+      : [resolve(apiRoot, '.env'), resolve(apiRoot, '.env.local')];
 
 for (const file of layers) {
   if (existsSync(file)) {
@@ -28,3 +42,6 @@ for (const file of layers) {
 if (!process.env.NODE_ENV) {
   process.env.NODE_ENV = nodeEnv;
 }
+if (!process.env.APP_ENV) {
+  process.env.APP_ENV = appEnv;
+}