feat(devops): 发版拆分为 client/site/server 三条独立流水线

将单一 CI/CD 流水线拆成三条互不影响的发布流水线，各有 tag 前缀、独立版本
序列与独立 CHANGELOG：

- client（client-v*）：Flutter 全平台 + version.yaml 自更新清单
- site（site-v*）：web/ Eleventy 营销站，不含 web 版 app
- server（server-v*）：backend Go 服务 + 共享基建 nginx/systemd

新增 3 个 workflow（deploy-client/site/server.yml）替换 deploy.yml；CI 脚本
按 part 拆分为 compile-/release-/deploy-{client,site,server}.sh，抽出公共函数
lib-forgejo.sh；compile-{macos,android,ios,windows}.sh 改去 client-v 前缀；
manual.yml 按前缀路由回滚。

跨流水线解耦：version.yaml 归 client，后端每请求实时读取（不重启、不触发
server 流水线）；官网下载页的版本徽章/下载链接/更新日志时间线运行时经
/api/v1/public/release 动态拉取（API 不可达回退构建时静态内容）。为此一次性
扩展后端 changelog 字段（version.go/public.go）与 download.njk 动态渲染。

CHANGELOG.md 重命名为 CHANGELOG-client.md，新增 CHANGELOG-site/server.md；
重写 /release 命令为 /release <part> [version]；同步更新 CLAUDE.md 与部署文档。

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

scripts/ci/test.sh

@@ -1,5 +1,8 @@
 #!/usr/bin/env bash
-# test.sh  —  run backend and frontend checks
+# test.sh [part]  —  run gate checks for a pipeline part.
+#   server  -> go test
+#   client  -> flutter analyze
+#   (none)  -> both (backwards compatible)
 set -euo pipefail
 
 export PATH="/opt/homebrew/bin:$PATH"
@@ -7,14 +10,28 @@ export GOPROXY="${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}"
 
-echo "==> test: go test"
-cd backend
-go test ./...
-cd ..
+PART="${1:-all}"
 
-echo "==> test: flutter analyze"
-cd client
-flutter analyze --no-fatal-infos --no-fatal-warnings
-cd ..
+run_server() {
+  echo "==> test: go test"
+  cd backend
+  go test ./...
+  cd ..
+}
+
+run_client() {
+  echo "==> test: flutter analyze"
+  cd client
+  flutter analyze --no-fatal-infos --no-fatal-warnings
+  cd ..
+}
+
+case "$PART" in
+  server) run_server ;;
+  client) run_client ;;
+  site)   echo "==> test: site has no test gate (build is the gate)" ;;
+  all)    run_server; run_client ;;
+  *)      echo "unknown part: $PART" >&2; exit 1 ;;
+esac
 
 echo "==> test: done"