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/reasons.ts

@@ -77,6 +77,16 @@ const REASONS: Record<string, ReasonText> = {
   space_insufficient: { text: "空间不足" },
   unidentifiable: { text: "没识别出作品" },
   user_deleted: { text: "已删除" },
+  // DL-3:还没提交就结束或在等的下载(计划的 statusReason、提交任务的延后原因)
+  cancelled_by_user: { text: "你取消了这个下载" },
+  approval_rejected: { text: "你没批准这个下载" },
+  approval_revoked: { text: "会话停止，下载没有提交" },
+  approval_expired: { text: "等批准超时，下载没有提交" },
+  subscription_reset: { text: "订阅重置时取消" },
+  automation_disabled: { text: "自动化已关闭", action: "在设置 → 自动化里打开" },
+  read_only_reconcile: { text: "只读对账中，暂不提交下载" },
+  rejected: { text: "下载器拒绝了这个种子" },
+  source_failed: { text: "从站点取种子失败", action: "检查站点登录后重新下载" },
 };
 
 /**