chore: move env examples to env-example/ and unify CDN env source

- Reorganize env example files into a dedicated env-example/ directory for clarity
- Update .gitignore to ignore env files (with examples now in env-example/)
- Unify CDN credentials (CF_ZONE_ID / CF_API_TOKEN) to be sourced from .env.local in both test and production deploys
- Update git_hooks/post-receive to copy production env example from new location
- Update deploy scripts (pre_release_web.sh, release_web.sh) to copy the appropriate env example into .env.local before building
- Update _deploy_lib.sh purge_cdn_cache to source from .env.local instead of .env

scripts/release/release_web.sh

@@ -18,6 +18,10 @@ cp -f icons/production/favicon.ico public/favicon.ico
 cp -f icons/production/icons/Icon-192.png public/images/icons/Icon-192.png
 cp -f icons/production/icons/Icon-512.png public/images/icons/Icon-512.png
 
+# 准备生产环境变量（env-example/.env.production.example → .env.local，供 purge_cdn_cache 读 CDN 凭据）
+echo "=== 准备生产环境变量（env-example/.env.production.example → .env.local） ==="
+cp -f env-example/.env.production.example .env.local
+
 echo "=== 执行构建部署脚本 ==="
 ./scripts/deploy/deploy_web.sh