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]>

apps/web/app/components/downloads/business-tasks.tsx

@@ -53,7 +53,7 @@ export const ACTIVE_TASK: TaskStatus[] = ["pending", "running", "waiting"];
 
 export const SUBJECT_LABEL: Record<string, string> = {
   download_task: "下载任务",
-  acquisition_plan: "下载计划",
+  acquisition_plan: "下载",
   acquisition_slot: "收录版本",
   organization_record: "整理记录",
   organize_request: "整理请求",
@@ -73,7 +73,7 @@ export function subjectLink(t: Pick<Task, "subjectType" | "subjectId">): string
     case "download_task":
       return consolePath("downloads", t.subjectId);
     case "acquisition_plan":
-      return consolePath("downloads", "plans");
+      return `${consolePath("downloads")}?plan=${encodeURIComponent(t.subjectId)}`;
     case "organization_record":
       return consolePath("organize", t.subjectId);
     case "media_entity":