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/deploy.env.example

@@ -4,8 +4,14 @@ DEPLOY_USER=root
 DEPLOY_PORT=22
 # DEPLOY_SSH_KEY=~/.ssh/id_rsa
 
+# 同机双栈目录
+PROD_APP_ROOT=/opt/dukang
+STAGING_APP_ROOT=/opt/dukang-staging
+# 兼容旧字段（未指定 --env 时可能用到）
 APP_ROOT=/opt/dukang
+
 # 生产仓库（SSH）
 GIT_REPO_URL=git@git.yqidian.com:jacy/dukang.git
 GIT_REMOTE=origin
-GIT_BRANCH=dev
+# 默认分支已由 --env 决定：staging→dev，production→main
+# GIT_BRANCH=dev