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/mock.ts

@@ -52,7 +52,7 @@ function script(goal: string, opts: AgentSessionOptions): Step[] {
   const steps: AgentPlanStep[] = [
     { id: "s1", title: "查本地库存和收录版本", status: "running", note: null },
     { id: "s2", title: "在站点搜 4K 候选", status: "pending", note: null },
-    { id: "s3", title: "选资源并生成下载计划", status: "pending", note: null },
+    { id: "s3", title: "选资源并准备下载", status: "pending", note: null },
     { id: "s4", title: "提交下载", status: "pending", note: null },
   ];
   let revision = 0;
@@ -324,7 +324,7 @@ function checkupSteps(goal: string, report: string): Step[] {
   ]);
 }
 
-/** 例 3:方案绑定下载计划(选定即批准),选了之后直接提交 */
+/** 例 3:方案绑定计划(选定即批准),选了之后直接提交 */
 const DUNE_PLAN = "00000000-0000-4000-8000-00000000b003";
 const DUNE_DECISION = "00000000-0000-4000-8000-00000000d003";
 function optionSteps(goal: string): Step[] {
@@ -338,7 +338,7 @@ function optionSteps(goal: string): Step[] {
         revision: 1,
         steps: [
           { id: "s1", title: "找 1080p 资源", status: "done", note: null },
-          { id: "s2", title: "生成下载计划", status: "done", note: null },
+          { id: "s2", title: "准备下载", status: "done", note: null },
           { id: "s3", title: "等你选方案", status: "running", note: null },
           { id: "s4", title: "提交下载", status: "pending", note: null },
         ],