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]>

CHANGELOG.md

@@ -10,6 +10,7 @@
 - 运行状态页进程表按道显示「运行中/并发 · 排队」与维护道让路状态;心跳照常记录事件循环延迟(将来拆进程的判据)。
 
 ### 变更
+- 下载计划并入下载面板(DL-3):去掉「下载计划」页签,旧地址(含 `?plan=` 与 `/downloads/plans/:id`)跳到下载面板并打开对应行;还没提交的下载作为「进行中」的行与下载任务按加入时间一起排并计入计数,状态写「等你批准」「等磁盘空间」「等开启自动化」「准备提交」,可直接批准 / 取消(等批准的同时在待处理里);下载详情新增「为什么下这个」(来源:订阅 / 智能体会话 / 手动;目的:补缺 / 升级(替换哪个版本)/ 换源;选中理由要点,原始评估进技术信息);没提交就结束的下载(失败 / 取消 / 过期)进作品的下载历史并写明原因;审批被拒、撤销或过期时草案随之结束。新增 `GET /acquisition-plans/{id}/why`、`POST /acquisition-plans/{id}/cancel`,面板接口行带 `kind`(task / plan)并支持 `planId`。界面与智能体能力标题不再出现"下载计划"(动作计数写"准备下载 N 个资源")。
 - `WORKER_CONCURRENCY` 从 io 组总并发改为映射到网络道;compose 不再给它缺省值(缺省走设置页)。`worker` / `worker:agent` / `all` 角色与镜像入口不变。
 
 ## [0.3.0] - 2026-09-29