refactor(契约): 判题状态码收进契约唯一一份，并收紧 18 处 as any

- 状态码常量与 judgeStatusSchema 移到 packages/contract/src/judge-status.ts，
  后端 judge/status.ts 只再导出；前端 SubmissionStatus 枚举加编译期断言对齐契约
  （实测改坏一个码会当场类型检查失败）
- 类型逃逸 22 处降到 4 处：collab/handler、pagination、configUpdate、
  ExerciseManager、ProblemSubmission、pk.vue tooltip；剩下的是词云插件无类型、
  生成的 .d.ts、skulpt 和 TextEditor

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/src/collab/handler.ts

@@ -198,6 +198,7 @@ export async function handleCollabMessage(ws: CollabSocket, raw: string) {
     studentId?: unknown
     language?: unknown
     reason?: unknown
+    timestamp?: unknown
   }
   try {
     message = JSON.parse(raw) as typeof message
@@ -213,9 +214,7 @@ export async function handleCollabMessage(ws: CollabSocket, raw: string) {
 
   // 心跳不查库，和 /ws/submissions 的处理一致
   if (message.type === "ping") {
-    ws.send(
-      JSON.stringify({ type: "pong", timestamp: (message as any).timestamp }),
-    )
+    ws.send(JSON.stringify({ type: "pong", timestamp: message.timestamp }))
     return
   }