refactor(前端): shared / utils 不再 import oj 和 admin 下的任何东西

依赖方向原来是反的：顶栏、登录框、举手列表这些 shared 组件从 oj/ 里拿东西。
- 跨端的接口挪进 shared/api.ts（按 apps/web/CLAUDE.md 的分法）：学生端题目列表、
  出题人列表、这节课的题、待弹的成就
- 这节课的 store → shared/store/lesson.ts；头像 RankAvatar → shared/components
- 纯函数挪进 utils/：举手列表的错法归类 errorKind、它依赖的答案错误分类 wrongAnswer
  和 Python 报错翻译 pythonError、题目列表行的 toProblemRow
- 只有后台在用的出题人下拉 AuthorSelect 挪回 admin/components

纯搬家。首页、题目列表、题目页、排名、课堂看板、后台题目列表打开无报错，
顶栏题号框敲 1001 回车直达题目页。

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

apps/web/src/shared/components/AuthorSelect.vue

@@ -1,33 +0,0 @@
-<template>
-  <n-select
-    style="width: 140px"
-    v-model:value="author"
-    remote
-    @update:show="getAuthorOptions"
-    :options="authorOptions"
-  />
-</template>
-
-<script setup lang="ts">
-import { getAuthors } from "oj/api"
-
-interface Props {
-  all?: boolean
-}
-
-const { all = false } = defineProps<Props>()
-
-const author = defineModel<string>("value")
-
-const authorOptions = ref([{ label: "全部", value: "" }])
-
-async function getAuthorOptions() {
-  authorOptions.value = [{ label: "全部", value: "" }]
-  const res = await getAuthors(all)
-  const remotes = res.map((item) => ({
-    label: `${item.username} (${item.problemCount})`,
-    value: item.username,
-  }))
-  authorOptions.value = [...authorOptions.value, ...remotes]
-}
-</script>

apps/web/src/shared/components/HelpRequestList.vue

@@ -1,6 +1,6 @@
 <script setup lang="ts">
 import { Icon } from "@iconify/vue"
-import { errorKind } from "oj/classroom/errorKind"
+import { errorKind } from "utils/errorKind"
 import { useBreakpoints } from "shared/composables/breakpoints"
 import { useTeacherHelp } from "shared/composables/teacherHelp"
 import { useCollabStore } from "shared/store/collab"

apps/web/src/shared/components/Login.vue

@@ -1,7 +1,7 @@
 <script setup lang="ts">
 import { Icon } from "@iconify/vue"
 import { useThemeVars } from "naive-ui"
-import RankAvatar from "oj/rank/components/RankAvatar.vue"
+import RankAvatar from "shared/components/RankAvatar.vue"
 import { classLabel, groupClassOptions } from "utils/classes"
 import { errorCode } from "utils/api"
 import { STORAGE_KEY } from "utils/constants"

apps/web/src/shared/components/ProblemJumpBox.vue

@@ -1,7 +1,7 @@
 <script setup lang="ts">
 import { Icon } from "@iconify/vue"
 import { useThemeVars } from "naive-ui"
-import { useLessonStore } from "oj/store/lesson"
+import { useLessonStore } from "shared/store/lesson"
 import { useProblemJump } from "shared/composables/problemJump"
 import { useUserStore } from "shared/store/user"
 import type { ClassActivityProblem } from "utils/types"

apps/web/src/shared/components/RankAvatar.vue

@@ -0,0 +1,79 @@
+<script setup lang="ts">
+import { useDark } from "@vueuse/core"
+import { rgba } from "shared/composables/tone"
+import { USERNAME_CLASS_RE } from "utils/constants"
+
+/**
+ * 排名页的头像。九成以上的学生没换过头像（1797 个号是 default.png），一排一模一样的
+ * 默认图分不出人，所以默认头像画成「名字最后一个字 + 彩色圆」，颜色按用户名固定 ——
+ * 同一个人在领奖台、赛道、「你」那张卡里是同一个颜色。自己是实心绿。
+ */
+const props = defineProps<{
+  username: string
+  avatar: string | null
+  size: number
+  me?: boolean
+}>()
+
+const isDark = useDark()
+/** 头像文件丢了（备份恢复后没拷上传目录、被删）就退回名字那个字，别露出破图 */
+const broken = ref(false)
+watch(
+  () => props.avatar,
+  () => (broken.value = false),
+)
+
+const PALETTE = ["#2f6fd0", "#c76a12", "#6a4bd8", "#0f7a6c", "#b4315f", "#4d5967", "#8a6a00"]
+
+const letter = computed(() => {
+  const name = props.username.replace(USERNAME_CLASS_RE, "") || props.username
+  return Array.from(name).at(-1) ?? "?"
+})
+
+const colors = computed(() => {
+  if (props.me) return { background: "#18a058", color: "#ffffff" }
+  let hash = 0
+  for (const char of props.username) hash = (hash * 31 + char.codePointAt(0)!) >>> 0
+  const base = PALETTE[hash % PALETTE.length]!
+  return { background: rgba(base, isDark.value ? 0.28 : 0.13), color: base }
+})
+</script>
+
+<template>
+  <img
+    v-if="avatar && !broken"
+    class="avatar"
+    :src="avatar"
+    alt=""
+    @error="broken = true"
+    :style="{ width: `${size}px`, height: `${size}px` }"
+  />
+  <span
+    v-else
+    class="avatar letter"
+    aria-hidden="true"
+    :style="{
+      width: `${size}px`,
+      height: `${size}px`,
+      fontSize: `${Math.round(size * 0.5)}px`,
+      ...colors,
+    }"
+    >{{ letter }}</span
+  >
+</template>
+
+<style scoped>
+.avatar {
+  border-radius: 50%;
+  flex-shrink: 0;
+  object-fit: cover;
+}
+
+.letter {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  font-weight: 700;
+  line-height: 1;
+}
+</style>