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>

deploy/ecosystem.config.cjs

@@ -1,5 +1,5 @@
 /** PM2 ecosystem — 杜康好客生产部署 */
-const APP_ROOT = '/opt/dukang';
+const APP_ROOT = process.env.APP_ROOT || '/opt/dukang';
 
 module.exports = {
   apps: [
@@ -11,6 +11,7 @@ module.exports = {
       exec_mode: 'fork',
       env: {
         NODE_ENV: 'production',
+        APP_ENV: 'production',
         PORT: 8090,
       },
     },
@@ -62,6 +63,7 @@ module.exports = {
       exec_mode: 'fork',
       env: {
         NODE_ENV: 'production',
+        APP_ENV: 'production',
       },
     },
   ],