feat(downloads): fold download plans into download panel (DL-3)

- Waiting plans (approval / disk space / automation off / queued) are
  active-segment rows on /download-tasks/board, merged by created_at,
  counted, with approve / cancel actions; ?plan= deep links and legacy
  /downloads/plans routes redirect to the panel
- Download detail shows "why this download" (source, purpose, replaced
  version, reasons); raw evaluation in tech info
- Failed / cancelled / expired plans appear in the entity download
  history; rejected / revoked / expired approvals close draft plans
- New GET /acquisition-plans/{id}/why, POST /acquisition-plans/{id}/cancel
- User-facing copy no longer says 下载计划; glossary updated

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/contracts/src/organization.ts

@@ -363,6 +363,13 @@ export const LibraryDownloadView = z.object({
 });
 export type LibraryDownloadView = z.infer<typeof LibraryDownloadView>;
 
+/** 没提交到下载器就结束的下载(DL-3):失败 / 取消 / 过期且没有下载任务的计划,进作品的下载历史 */
+export const LibraryDroppedPlanView = z.object({
+  plan: AcquisitionPlan,
+  releaseTitle: z.string().nullable(),
+});
+export type LibraryDroppedPlanView = z.infer<typeof LibraryDroppedPlanView>;
+
 export const LibraryDetail = z.object({
   entity: MediaEntity,
   /** 身份映射状态(含 proposed/conflicted,前端区分展示) */
@@ -374,6 +381,7 @@ export const LibraryDetail = z.object({
   slots: z.array(AcquisitionSlot),
   candidates: z.array(CandidateEvaluation),
   downloads: z.array(LibraryDownloadView),
+  droppedPlans: z.array(LibraryDroppedPlanView).default([]),
   /**
    * 该作品的整理记录(最近 100 条,新→旧):含没有下载任务的手动整理(文件管理按路径整理)。
    * 下载历史里已按下载任务列出的记录也在这里,前端按 downloadTaskId 去重展示。