feat(downloads): live speeds and active/completed split on the download panel (DL-2)

- GET /download-tasks/board?state=active|completed: per-torrent dl/up speed,
  ETA, seeds/leechs, downloader total speed (transfer/info), counts for both
  groups, latest organize result (status, reason code, open decision)
- live qB data cached per instance for 2 s with in-flight coalescing
- panel: total speed line, 进行中 / 已完成 segments remembered locally,
  4 s polling while the page is visible, mobile layout, "—" for zero speed

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/contracts/src/api.ts

@@ -8,6 +8,7 @@ import { MetadataEnrichOutput, WebSearchTestInput, WebSearchTestResult } from ".
 import { CapabilityDescriptor, KnownCapabilityId } from "./capability.ts";
 import { type ApiScope, CursorQuery, cursorPage, HealthStatus, Id, IdParam } from "./common.ts";
 import * as content from "./content.ts";
+import * as board from "./download-board.ts";
 import * as events from "./events.ts";
 import * as execution from "./execution.ts";
 import * as files from "./files.ts";
@@ -1132,6 +1133,15 @@ export const Api = {
       },
       R,
     ),
+    board: ep({
+      method: "get",
+      path: "/download-tasks/board",
+      scope: "read",
+      summary:
+        "下载面板：按进行中 / 已完成分组列出下载任务，附每个种子的实时速度、剩余时间、连接数与下载器总速度（实时数据短时缓存）",
+      query: board.DownloadBoardQuery,
+      response: board.DownloadBoard,
+    }),
     pause: ep({
       method: "post",
       path: "/download-tasks/{id}/pause",