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-timeline.tsx

@@ -10,7 +10,7 @@ import { Timeline } from "~/components/console/timeline.tsx";
 
 export const STAGE_LABEL: Record<TimelineStage, string> = {
   observation: "发现",
-  plan: "计划",
+  plan: "准备",
   download: "下载",
   organization: "整理",
   agent: "智能体",