feat(提交列表): 题号填错一道时顶上提示「没有这道题」；← → 也能翻上一条下一条

- 列表接口回带查不到的题号（公开列表只认公开题，比赛列表只认本场的题），
  一次填好几道时打错的那道原来被悄悄忽略
- 方向键恢复成四个都能翻（9 月加的时候就是这样，老师已经用惯了）

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

packages/contract/src/flowchart.ts

@@ -58,7 +58,10 @@ export const flowchartListItemSchema = z.object({
   showLink: z.boolean(),
 })
 
-export const flowchartListSchema = paginatedSchema(flowchartListItemSchema)
+export const flowchartListSchema = paginatedSchema(flowchartListItemSchema).extend({
+  /** 题号框里查不到的题号，口径同 submissionListSchema.unknownProblems */
+  unknownProblems: z.array(z.string()),
+})
 export const createFlowchartResponseSchema = z.object({
   submissionId: z.string(),
   status: z.literal("pending"),