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/agent/agent-interaction.tsx

@@ -298,7 +298,7 @@ export function OptionsCard({ runId, view, waiting }: { runId: string; view: Opt
 
 const RISK_LABEL: Record<RiskLevel, string> = { low: "低", medium: "中", high: "高" };
 const PLAN_LABEL: Record<string, string> = {
-  acquisition_plan: "下载计划",
+  acquisition_plan: "下载",
   organize_plan: "整理计划",
   policy_revision: "策略版本",
 };