feat(downloads): 多下载器路由:默认下载器、站点指定下载器、别名

照 MP(chain/download/submission.py:明确指定 or 站点下载器 or 默认):
- 迁移 0063:downloader_instance.is_default(至多一个,唯一索引)、site.downloader_instance_id
- pickInstance:明确指定 > 站点指定 > 默认 > 第一个可用;自动下载(gates)与手动下载共用
- 设置:下载器名称改称别名,新增「设为默认下载器」;站点编辑新增「下载器」选择
- 测试 downloader-routing.test.ts

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

apps/web/app/components/sites/site-dialogs.tsx

@@ -3,6 +3,7 @@ import { CircleCheck, CircleX, KeyRound, LoaderCircle, TriangleAlert } from "luc
 import { useState } from "react";
 import { Link } from "react-router";
 import { toast } from "sonner";
+import { downloaders } from "~/api/instances.ts";
 import {
   useDeleteSite,
   useHealthCheck,
@@ -25,6 +26,7 @@ import {
   DialogTitle,
 } from "~/components/ui/dialog.tsx";
 import { Input } from "~/components/ui/input.tsx";
+import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from "~/components/ui/select.tsx";
 import { Switch } from "~/components/ui/switch.tsx";
 import { errorMessage } from "~/lib/api.ts";
 import { cn } from "~/lib/utils.ts";
@@ -323,8 +325,11 @@ export function CredentialDialog({
 }
 
 /** 编辑抽屉:名称、域名、限流(空 = 站点默认)、定时快照、代理 */
+const DEFAULT_DOWNLOADER = "__default__";
+
 export function SiteEditSheet({ site, onClose }: { site: SiteListItem; onClose: () => void }) {
   const update = useUpdateSite();
+  const dl = downloaders.useList();
   const [v, setV] = useState({
     name: site.name,
     baseUrl: site.baseUrl,
@@ -334,6 +339,7 @@ export function SiteEditSheet({ site, onClose }: { site: SiteListItem; onClose:
     intervalMin: site.snapshotIntervalSec ? String(Math.round(site.snapshotIntervalSec / 60)) : "",
     proxy: site.proxy,
     searchDefault: site.searchDefault !== false,
+    downloader: site.downloaderInstanceId ?? DEFAULT_DOWNLOADER,
   });
   const [errors, setErrors] = useState<Record<string, string>>({});
   const set = <K extends keyof typeof v>(k: K, val: (typeof v)[K]) => setV((s) => ({ ...s, [k]: val }));
@@ -376,6 +382,7 @@ export function SiteEditSheet({ site, onClose }: { site: SiteListItem; onClose:
           snapshotIntervalSec: interval ? interval * 60 : null,
           proxy: v.proxy,
           searchDefault: v.searchDefault,
+          downloaderInstanceId: v.downloader === DEFAULT_DOWNLOADER ? null : v.downloader,
         },
       });
       toast.success(`${v.name.trim()} 已保存`);
@@ -458,6 +465,27 @@ export function SiteEditSheet({ site, onClose }: { site: SiteListItem; onClose:
             />
           </FormField>
         ) : null}
+        <FormField
+          label="下载器"
+          htmlFor="se-downloader"
+          hint="这个站的资源用哪个下载器；订阅或手动下载时明确指定的下载器优先"
+        >
+          <Select value={v.downloader} onValueChange={(x) => set("downloader", x)} disabled={busy}>
+            <SelectTrigger id="se-downloader" className="w-full">
+              <SelectValue />
+            </SelectTrigger>
+            <SelectContent position="popper">
+              <SelectItem value={DEFAULT_DOWNLOADER}>默认下载器</SelectItem>
+              {(dl.data?.items ?? []).map((d) => (
+                <SelectItem key={d.id} value={d.id}>
+                  {d.name}
+                  {d.isDefault ? "（默认）" : ""}
+                  {d.enabled ? "" : "（已停用）"}
+                </SelectItem>
+              ))}
+            </SelectContent>
+          </Select>
+        </FormField>
         <div className="mb-2 flex items-start gap-3">
           <Switch id="se-proxy" checked={v.proxy} onCheckedChange={(x) => set("proxy", x)} disabled={busy} />
           <label htmlFor="se-proxy" className="text-caption">