ci: 运行环境自愈预置 + 发版任务串行 + 删 ci.yml/暂停备份

- 新增 scripts/ci/provision-{mac,windows}.sh：幂等预置，按 Flutter 版本
  stamp 短路，pipeline 首跑自动 precache + 预热缓存，运行时不再下载 engine
- scripts/ci/_env.sh：抽出共用镜像 env，compile 脚本统一 source
- deploy.yml：build-macos needs build-linux-web，同一 mac runner 串行
  执行，避免排队超时；各 build job 加 Provision 前置步骤
- 删除 .gitea/workflows/ci.yml
- backup.yml：暂停定时备份（保留 workflow_dispatch 手动触发）

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/ci/compile.sh

@@ -2,10 +2,8 @@
 # compile.sh <tag>  —  build backend + Flutter web, package into dist/
 set -euo pipefail
 
-export PATH="/opt/homebrew/bin:$PATH"
-export GOPROXY="${GOPROXY:-https://goproxy.cn,direct}"
-export PUB_HOSTED_URL="${PUB_HOSTED_URL:-https://pub.flutter-io.cn}"
-export FLUTTER_STORAGE_BASE_URL="${FLUTTER_STORAGE_BASE_URL:-https://storage.flutter-io.cn}"
+# shellcheck source=scripts/ci/_env.sh
+. "$(dirname "$0")/_env.sh"
 
 TAG="$1"
 VER="${TAG#v}"