Add graceful SCUM stop, restart, and version update flow

SCUM 停止/重启/更新以前只有“结束进程”这一条路，插件没有声明任何优雅关闭方式，
平台也没有把停止后重新启动串起来。现在插件声明自己的关闭脚本，run 先执行它，
平台在停止或更新成功后再自动拉起服务。

run:
- lifecycle stop 支持插件声明的 gracefulStop（可执行文件、参数、环境、超时、
  fallback=report|terminate）；关闭命令超时且声明 report 时任务失败，不再默默杀进程。
- 新增 steam.update 依赖探针：调用 steamcmd +app_info_print 获取公开分支 buildid，
  与本地 steamapps/appmanifest_<appid>.acf 的 buildid 比较，输出
  installed/latest/update=yes|no|unknown。

platform:
- 新增 POST /api/v1/server-instances/{id}/restart 与 /update。
- restart 派发插件 stop 动作（走优雅关闭），终态成功后入队 start 作业。
- update 派发插件 install 动作；插件在更新前必须先优雅关闭 SCUM，关闭失败直接拒绝
  SteamCMD 更新，成功后平台再拉起服务。
- 依赖检查输入带上插件声明的服务器安装根目录，供 steam.update 读取 appmanifest。

plugin (SCUM server plugin 0.1.16):
- bin/scum-stop.cmd：解析已声明的可执行文件路径，定位同路径正在运行的 SCUMServer.exe，
  通过本地 RCON 公告并发送关闭命令，等待进程自行退出；不再使用 taskkill。
- bin/scum-rcon.ps1：插件自有的 Source RCON 客户端，从 UE4SS mod config.ini 读取
  密码/端口，密钥不离开本机。
- actions/stop.json 声明 gracefulStop；actions/install.json 更新前先执行同一关闭脚本。

platform_web:
- 服务器详情新增“重启”按钮和“SCUM 版本更新”面板；点“检查更新”查询公开分支版本，
  只有检测到更新时“更新版本”按钮才会置为可用并高亮，点击后先确认再派发更新任务。

platform_web/contracts/pages.md

@@ -23,7 +23,7 @@ Default landing page for server owners and server administrators. Shows searchab
 
 ## 服务器详情
 
-Daily operations hub for one server. Status header shows online state, player count, TPS, latency, CPU/memory/disk progress, metric freshness, and confirmed start/stop lifecycle actions. Plugin-declared pages render as first-class server tabs before platform sections, so each game owns its safe menu surface; SCUM user and vehicle pages read platform-maintained SCUM tables while plugin-owned squads, map settings, gifts, and workflows stay in scoped plugin records. Built-in sections are 管理 (deployment status, metadata, administrators) and AI 助手 (LLM suggestions produce reviewable config diffs or typed workflow drafts; no raw AI keys reach the frontend). Raw logs, management terminal/RCON input, arbitrary config workbench, generic operation history, runtime-binding, and generic plugin-control tabs must not be exposed in server detail.
+Daily operations hub for one server. Status header shows online state, player count, TPS, latency, CPU/memory/disk progress, metric freshness, and confirmed start, stop, restart, and plugin-declared graceful-update lifecycle actions, plus a game-version module that checks the plugin-declared Steam build probe and only lights up the update action when a newer public build is reported. Plugin-declared pages render as first-class server tabs before platform sections, so each game owns its safe menu surface; SCUM user and vehicle pages read platform-maintained SCUM tables while plugin-owned squads, map settings, gifts, and workflows stay in scoped plugin records. Built-in sections are 管理 (deployment status, metadata, administrators) and AI 助手 (LLM suggestions produce reviewable config diffs or typed workflow drafts; no raw AI keys reach the frontend). Raw logs, management terminal/RCON input, arbitrary config workbench, generic operation history, runtime-binding, and generic plugin-control tabs must not be exposed in server detail.
 
 ## 插件市场