feat(web): W3-3 site workbench, sources/feeds/snapshots, downloads with business timeline, organization records and agent sessions

- sites + /sites/:siteId: organized view with snapshot-first release list, inventory overlay,
  candidate reasons, volatile-field recheck, stale marking that keeps existing data, live search,
  unified download entry; origin view placeholder (M2)
- sources: feed CRUD/enable/fetch/reset, cursor/health/gap hints; per-site snapshot history
- tasks: download tasks with pause/resume (threshold pause cannot be bypassed), plans,
  cache volume thresholds and cleanup, business timeline (observation → plan → download →
  organization → agent/engine)
- organize: record list/detail with file-level results, manual organize with dryRun preview
- agent: session list/page and layout drawer with context prefix; streaming events,
  tool cards, rejection alerts, compaction, budget meters, model text vs server report;
  mock switch (?mock=1) until W2-D endpoints land

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

apps/web/app/routes/console/tasks.$id.tsx

@@ -1,6 +1,38 @@
-import { WorkspacePlaceholder } from "~/components/console/workspace-placeholder.tsx";
+import { ArrowLeft } from "lucide-react";
+import { Link, useParams } from "react-router";
+import { useDownloadTask } from "~/api/downloads.ts";
+import { ErrorState, LoadingState } from "~/components/console/empty-state.tsx";
+import { PageHeader } from "~/components/console/page-header.tsx";
+import { DownloadDetail } from "~/components/downloads/download-detail.tsx";
+import { Button } from "~/components/ui/button.tsx";
 
-// 占位:路由已在 app/routes.ts 登记,由对应工作区负责实现
-export default function Page() {
-  return <WorkspacePlaceholder />;
+export default function DownloadTaskPage() {
+  const { id = "" } = useParams();
+  const task = useDownloadTask(id);
+  return (
+    <>
+      <PageHeader
+        title={task.data?.name ?? "下载任务"}
+        description="下载 → 整理 → 核验的业务时间线与子任务"
+        className="[&_h1]:break-all"
+        actions={
+          <Button asChild variant="ghost" size="sm">
+            <Link to="/console/tasks">
+              <ArrowLeft />
+              下载与任务
+            </Link>
+          </Button>
+        }
+      />
+      <div className="pg-slab rounded-xl p-4 md:p-5">
+        {task.isPending ? (
+          <LoadingState rows={5} />
+        ) : task.error ? (
+          <ErrorState plain error={task.error} onRetry={() => void task.refetch()} />
+        ) : (
+          <DownloadDetail task={task.data} />
+        )}
+      </div>
+    </>
+  );
 }