chore: add .env.example template and clean up deploy messages

Introduce a tracked .env.example file documenting all required environment
variables (app env, API/WebSocket base URLs, timeouts, Google/Facebook OAuth
credentials, Cloudflare CDN zone/token). Update .gitignore to allow this
file despite the blanket .env* ignore rule. Also simplify the push
success/failure output in scripts/deploy/_deploy_lib.sh by removing
verbose troubleshooting hints.

scripts/deploy/_deploy_lib.sh

@@ -34,13 +34,11 @@ push_to_server() {
 
     if [ $? -eq 0 ]; then
         echo "=========================================="
-        echo "推送成功！服务器端 post-receive hook 应已自动执行"
+        echo "推送成功！"
         echo "=========================================="
     else
         echo "=========================================="
-        echo "推送失败！常见原因："
-        echo "  1. 本地分支与远端非 fast-forward（git pull --rebase 后再试）"
-        echo "  2. 服务器端 hook 报错（看 git push 输出）"
+        echo "推送失败！"
         echo "=========================================="
         return 1
     fi