feat: 补齐第一批已知缺口（关闭握手 / 定时备份 / Origin 白名单 / DTO 收敛）

- httpapi：新增 POST /api/shutdown（admin 会话或 X-Shutdown-Token 常量时间比对）
  与 GET /api/rules/switches（recorder 可读，只回布尔开关）；settings/standings 的
  重复 DTO 收敛到 internal/dto；standings.showIndividualMedals 贯通到设置读写与前端
- export：抽出 export.Service，新增自动备份定时任务（backup.intervalMinutes/keep），
  自动、手动、发布前三类备份共用同一把互斥锁与滚动清理
- realtime：/ws 去掉 InsecureSkipVerify，改用 OriginPatterns（同源与无 Origin 放行，
  跨站需命中 server.allowedOrigins）
- console：停止服务改走 POST /api/shutdown 优雅关闭（5 秒宽限后回退强杀），
  服务管理器新增「已连接的大屏实例」卡片
- deploy：build.bat 改用 for /f 读内部署名——set /p 在 chcp 65001 下返回空，
  导致最近这次构建的 exe 里根本没注入署名
- docs：备份策略、关闭超时、Origin 配置的说明与实现对齐

deploy/build.bat

@@ -29,9 +29,10 @@ cd ..
 echo === [3/4] server build ===
 cd server
 if not exist ..\dist mkdir ..\dist
-REM internal signature is injected from a machine-local file (gitignored, never in repo)
+REM internal signature is injected from a machine-local file (gitignored, never in repo).
+REM set /p returns empty under chcp 65001, so read the first line with for /f instead.
 set "INTERNAL_SIGNATURE="
-if exist "..\deploy\signature.local.txt" set /p INTERNAL_SIGNATURE=<"..\deploy\signature.local.txt"
+if exist "..\deploy\signature.local.txt" for /f "usebackq delims= eol=" %%A in ("..\deploy\signature.local.txt") do if not defined INTERNAL_SIGNATURE set "INTERNAL_SIGNATURE=%%A"
 if defined INTERNAL_SIGNATURE (
   REM single quotes keep spaces inside the value intact for go's ldflags parser
   go build -ldflags "-X 'git.yeij.top/AskaEth/Scoreboard/server/internal/version.InternalSignature=%INTERNAL_SIGNATURE%'" -o ..\dist\scoreboard.exe . || exit /b 1