feat(frontend): 来源弹窗加loading + 笔记页暗色适配 + 主题透传

- 来源上传弹窗 A系统基因库 tab 搜索时显示 loading spinner
- NetworkActor 组件初始加载时显示 loading spinner（初始状态设为 true）
- StudioNotebooksPage 笔记卡片支持暗色主题样式
- StudioNotebookDetailPage / NotebookAIWritingPage 跳转时透传 themekey 参数

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend-web/src/components/assistant-ui/document-upload-popup.tsx

@@ -826,7 +826,13 @@ const DocumentUploadPopupContent: FC<{
                         </Button>
                       </div>
                     )}
-                    {listData.length === 0 && <Empty />}
+                    {isSearching ? (
+                      <div className="flex items-center justify-center py-16">
+                        <Loader2 className="h-8 w-8 animate-spin text-muted-foreground" />
+                      </div>
+                    ) : (
+                      listData.length === 0 && <Empty />
+                    )}
                     {searchType === "human" && (
                       <div className="bg-white p-[10px] grid grid-cols-5 gap-[10px]">
                         {listData.map((item: listDataItem, index: number) => {

frontend-web/src/components/assistant-ui/network-actor.tsx

@@ -545,7 +545,12 @@ export function NetworkActor({ inputValue, searchSpaceId, onSuccess }: NetworkAc
           </div>
         )}
         <div className="p-[10px]">
-          <div className="grid grid-cols-4 gap-[10px] user-list">
+          {isSearching ? (
+            <div className="flex items-center justify-center py-16">
+              <Loader2 className="h-8 w-8 animate-spin text-muted-foreground" />
+            </div>
+          ) : null}
+          <div className={`grid grid-cols-4 gap-[10px] user-list${isSearching ? ' hidden' : ''}`}>
             {userList.map((item, index) => (
               <div key={index} className="user-item p-[10px] relative">
                 <div className="absolute top-[5px] right-[10px]">