refactor: repartition server-side and client-side code

app/.client/stores/previews.ts

@@ -0,0 +1,39 @@
+import { atom } from 'nanostores';
+import type { ExportEditorFile } from './web-builder';
+
+export interface PreviewInfo {
+  content: string;
+  filename: string;
+  mimeType: string;
+}
+
+// 当页面保存时，由 save 方法主动调用并 setPreviews 来更新 previews 中的数据
+export class PreviewsStore {
+  previews = atom<PreviewInfo[]>([]);
+  currentPreview = atom<string | null>(null);
+
+  setPreviews(files: ExportEditorFile[]) {
+    this.previews.set(
+      files.map((file) => ({
+        content: file.content,
+        filename: file.filename,
+        mimeType: file.mimeType,
+      })),
+    );
+  }
+
+  setCurrentPreview(filename: string) {
+    this.currentPreview.set(filename);
+  }
+}
+
+// Create a singleton instance
+let previewsStore: PreviewsStore | null = null;
+
+export function usePreviewStore() {
+  if (!previewsStore) {
+    previewsStore = new PreviewsStore();
+  }
+
+  return previewsStore;
+}