chore(构建): Bun 锁到 1.4.4，CI 和镜像不再跟 latest；后端类型检查换成 bun check

单二进制把运行时一起打进去，CI 装的是几线上就是几，之前三处都不锁（@types/bun latest、
setup-bun latest、oven/bun:1），1.4.x 每版都有破坏性变更会悄悄上线。
顺带 bunfig 加 minimumReleaseAge = "3d"，@types/bun 除外。
后端 typecheck 从 tsc 换成 bun check，1.9s → 0.26s，报错一致。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package.json

@@ -1,6 +1,7 @@
 {
   "name": "oj2",
   "private": true,
+  "packageManager": "bun@1.4.4",
   "type": "module",
   "workspaces": ["apps/*", "packages/*"],
   "scripts": {
@@ -18,7 +19,7 @@
     "check": "vp check"
   },
   "devDependencies": {
-    "@types/bun": "latest",
+    "@types/bun": "1.4.4",
     "typescript": "^5.9.3",
     "vite-plus": "^1.0.0-rc.1"
   }