refactor(release): 改为 Agent 双阶段人工发布

删除 Gitea Actions、Tag/Main 自动流水线和旧 Runner 配置，取消 Git 操作与发布授权的绑定。\n\n新增本地镜像发布、固定生产部署助手、digest manifest、迁移安全检查、simulation 冒烟及显式回滚流程。\n\n验证：pnpm lint、pnpm test、pnpm build、Go 全量测试、ShellCheck、Compose 配置、人工发布测试和 linux/amd64 完整栈冒烟。

deploy/manual/easyai-ai-gateway-release.conf.example

@@ -0,0 +1,12 @@
+# Install as /etc/easyai-ai-gateway-release.conf with mode 0600 and root ownership.
+DEPLOY_DIR=/root/easyai-ai-gateway-deploy
+COMPOSE_FILE=/root/easyai-ai-gateway-deploy/docker-compose.yml
+RELEASES_DIR=/root/easyai-ai-gateway-deploy/.releases
+BACKUP_DIR=/var/backups/easyai-ai-gateway
+PUBLIC_BASE_URL=https://ai.51easyai.com
+API_PORT=8088
+WEB_PORT=5178
+POSTGRES_SERVICE=postgres
+POSTGRES_USER=easyai
+POSTGRES_DATABASE=easyai_ai_gateway
+BACKUP_RETENTION=5