修复无板块时空态导航失效，去除发帖本地草稿，并种子默认板块。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/pages/HomePage.tsx

@@ -258,6 +258,7 @@ export default function HomePage() {
           keyword={keyword}
           boardId={boardId}
           boardName={ctx?.boards?.find(b => b.id === boardId)?.name || ''}
+          noBoards={!ctx?.boardsLoading && (ctx?.boards?.length ?? 0) === 0}
         />
       </div>
     </div>