refactor(提交列表): 选中翻阅、实时更新、「这节课」、带条件去统计拆成四个 composable

list.vue 从 1834 行减到 1604 行，拆出 oj/submission/composables/ 下的
rowCursor（↑ ↓ 换条、页头页尾自动翻页）、listLive（正在评分的 3 秒刷新、第一页的
「有 N 条新提交」）、lessonFilter（「这节课」一键筛）、statsLink（和统计之间来回带条件）。
注释原样跟着走。

纯搬家。七个状态（列表、↓↓、↑、流程图、我的、手机列表、手机详情）改前改后截图一致；
连按 31 下 ↓ 翻到第 2 页，别人交一条后 18 秒内出「有 1 条新提交」，「这节课」筛到
班级 + 题号 + 今天。

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

apps/web/src/oj/submission/composables/listLive.ts

@@ -0,0 +1,90 @@
+import { computed, ref, type Ref } from "vue"
+import { useDocumentVisibility, useIntervalFn } from "@vueuse/core"
+import { SubmissionStatus } from "utils/constants"
+import {
+  FlowchartSubmissionStatus,
+  type FlowchartSubmissionListItem,
+  type SubmissionListItem,
+} from "utils/types"
+import type { Row, SubmissionQuery } from "./listQuery"
+
+function isPending(row: Row) {
+  if ("result" in row) {
+    return row.result === SubmissionStatus.pending || row.result === SubmissionStatus.judging
+  }
+  return (
+    row.status === FlowchartSubmissionStatus.PENDING ||
+    row.status === FlowchartSubmissionStatus.PROCESSING
+  )
+}
+
+/**
+ * 提交列表的实时更新。两件事，一个定时器：
+ * - 本页有「正在评分」的，3 秒拉一次，把结果原地换上；
+ * - 第一页每 15 秒看一眼有没有新交的。**新的不直接插进来** —— 老师正看着第 5 行，
+ *   上面突然塞进 3 行，选中的那行就跑了。顶上给一条「有 N 条新提交」，点了才换。
+ * 页面切到后台就停。
+ *
+ * `requestSeq` 是列表那边的请求序号：拉的这期间筛选变了、翻页了，这份结果就作废。
+ */
+export function useListLive(options: {
+  query: SubmissionQuery
+  flowMode: Ref<boolean>
+  rows: Ref<Row[]>
+  submissions: Ref<SubmissionListItem[]>
+  flowcharts: Ref<FlowchartSubmissionListItem[]>
+  loading: Ref<boolean>
+  loaded: Ref<boolean>
+  fetchPage: () => Promise<{ results: Row[] }>
+  requestSeq: () => number
+}) {
+  const { query, flowMode, rows, submissions, flowcharts } = options
+  const newCount = ref(0)
+  const newCountCapped = computed(() => newCount.value >= query.limit)
+  let lastPoll = Date.now()
+  const visibility = useDocumentVisibility()
+
+  const hasPending = computed(() => rows.value.some(isPending))
+
+  useIntervalFn(async () => {
+    if (visibility.value !== "visible" || options.loading.value || !options.loaded.value) return
+    const interval = hasPending.value ? 3000 : 15000
+    if (Date.now() - lastPoll < interval) return
+    if (!hasPending.value && query.page !== 1) return
+    lastPoll = Date.now()
+    const seq = options.requestSeq()
+    const mode = flowMode.value
+    let res
+    try {
+      res = await options.fetchPage()
+    } catch {
+      return
+    }
+    // 这期间筛选变了、翻页了，这份结果就作废
+    if (seq !== options.requestSeq() || mode !== flowMode.value) return
+    const fresh = new Map<string, Row>(res.results.map((row) => [row.id, row]))
+    if (mode) {
+      flowcharts.value = flowcharts.value.map(
+        (row) => (fresh.get(row.id) as FlowchartSubmissionListItem | undefined) ?? row,
+      )
+    } else {
+      submissions.value = submissions.value.map(
+        (row) => (fresh.get(row.id) as SubmissionListItem | undefined) ?? row,
+      )
+    }
+    if (query.page === 1) {
+      const current = new Set(rows.value.map((row) => row.id))
+      const newest = rows.value[0]?.createTime ?? ""
+      newCount.value = res.results.filter(
+        (row) => !current.has(row.id) && row.createTime > newest,
+      ).length
+    }
+  }, 1000)
+
+  /** 刚点了重新判题 / 重新评分：下一秒就拉，不等满 3 秒 */
+  function pollSoon() {
+    lastPoll = 0
+  }
+
+  return { newCount, newCountCapped, pollSoon }
+}