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/settings/instances.tsx

@@ -102,16 +102,21 @@ function DownloadersTable() {
       config={{
         noun: "下载器实例",
         description:
-          "只接管带管理标签的任务。多个实例共用一块缓存盘时填相同的缓存卷标识，水位合并计算。点行编辑实例和路径映射。",
+          "只接管带管理标签的任务。可添加多个下载器：订阅或手动下载指定了下载器就用指定的，否则用站点指定的，再否则用默认下载器。多个实例共用一块缓存盘时填相同的缓存卷标识，水位合并计算。点行编辑实例和路径映射。",
         emptyHint: "添加 qBittorrent 后才能提交下载。",
         drawerExtra: (r) => <PathMappingsPanel viewKind="downloader" instanceId={r.id} />,
         columns: [
           {
             key: "name",
-            header: "名称",
+            header: "别名",
             cell: (r) => (
               <div className="min-w-0">
-                <p className="font-medium">{r.name}</p>
+                <p className="font-medium">
+                  {r.name}
+                  {r.isDefault ? (
+                    <span className="ml-1.5 font-normal text-meta text-muted-foreground">默认</span>
+                  ) : null}
+                </p>
                 <p className="truncate text-meta text-muted-foreground">{r.baseUrl}</p>
               </div>
             ),
@@ -128,7 +133,7 @@ function DownloadersTable() {
         ],
         rowActions: (r) => <TestButton pending={test.isPending} run={() => test.mutateAsync(r.id)} />,
         fields: [
-          { name: "name", label: "名称", kind: "text", required: true, placeholder: "例如：家里的 qB" },
+          { name: "name", label: "别名", kind: "text", required: true, placeholder: "例如：家里的 qB、番剧专用" },
           {
             name: "baseUrl",
             label: "WebUI 地址",
@@ -161,6 +166,12 @@ function DownloadersTable() {
           },
           { name: "managedTag", label: "管理标签", kind: "text", placeholder: "umt", hint: "只接管带此标签的任务" },
           { name: "cacheVolumeKey", label: "缓存卷标识", kind: "text", placeholder: "cache-1" },
+          {
+            name: "isDefault",
+            label: "设为默认下载器",
+            kind: "switch",
+            hint: "订阅、手动下载和站点都没指定下载器时用它；只能有一个默认",
+          },
           { name: "enabled", label: "启用", kind: "switch" },
         ],
         initial: {
@@ -172,6 +183,7 @@ function DownloadersTable() {
           apiKey: "",
           managedTag: "umt",
           cacheVolumeKey: "",
+          isDefault: false,
           enabled: true,
         },
         fromRow: (r) => ({
@@ -185,6 +197,7 @@ function DownloadersTable() {
           "secret:authKind": authKindOf(r),
           managedTag: r.managedTag,
           cacheVolumeKey: r.cacheVolumeKey ?? "",
+          isDefault: r.isDefault,
           enabled: r.enabled,
         }),
         toBody: (v: FormValues, mode) => ({
@@ -201,6 +214,7 @@ function DownloadersTable() {
                 : undefined,
           managedTag: optStr(v.managedTag),
           cacheVolumeKey: nullStr(v.cacheVolumeKey),
+          isDefault: v.isDefault === true,
           enabled: v.enabled === true,
         }),
         createSchema: DownloaderInstanceCreate,