feat: 重新设计作品展管理

- 作品改成缩略图卡片：手动排序时用 ← → 调整顺序，有新提交的显示“换成最新的”，
  点缩略图在抽屉里打开批改面板，撤下用页面内确认
- 奖项列表可以上下调整顺序（不用再填排序数字）；设置有改动才能保存；删除奖项说明会撤下几件作品
- 去掉按提交 ID 添加作品（前端、类型和 /manage/submissions 接口），改为提示在批改面板里“加入作品展”
- 管理接口返回作品代码，画缩略图用

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

server/src/routes/showcase.ts

@@ -41,6 +41,10 @@ function itemManageOut(r: any) {
     awarded_at: iso(r.awarded_at),
     has_prompt_chain: bool(r.has_prompt_chain),
     is_stale: bool(r.is_stale),
+    // 管理页的缩略图要用
+    html: r.html,
+    css: r.css,
+    js: r.js,
   }
 }
 
@@ -164,32 +168,6 @@ router.delete("/manage/awards/:award_id", (c) => {
   return c.json({ message: "删除成功" })
 })
 
-router.get("/manage/submissions/:submission_id", (c) => {
-  requireAdmin(c)
-  const id = uuidParam(c, "submission_id")
-  const s = orNotFound(
-    get(
-      `SELECT s.id, u.username, t.title AS task_title, t.display AS task_display, t.task_type,
-         s.score, s.view_count, ${HAS_CHAIN}
-       FROM submission_submission s
-       JOIN account_user u ON u.id = s.user_id
-       JOIN task_task t ON t.id = s.task_id
-       WHERE s.id = $id`,
-      { id },
-    ),
-  )
-  return c.json({
-    submission_id: uuidOut(s.id),
-    username: s.username,
-    task_title: s.task_title,
-    task_display: s.task_display,
-    task_type: s.task_type,
-    score: s.score,
-    view_count: s.view_count,
-    has_prompt_chain: bool(s.has_prompt_chain),
-  })
-})
-
 router.get("/manage/awards/:award_id/items", (c) => {
   requireAdmin(c)
   const award = orNotFound(