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

git_hooks/post-receive

@@ -8,7 +8,7 @@
 #   - 内部 = `npm run build && npm run start`
 #   - 实际调用 `pnpm run build:start`（项目使用 pnpm）
 
-# 准备生产环境变量（从 .env.production.example 复制 → .env.production）
-cp -f .env.production.example .env.production
+# 准备生产环境变量（从 env-example/.env.production.example 复制 → .env.production）
+cp -f env-example/.env.production.example .env.production
 
 pnpm run build:start