✨(frontend) add multi columns support for editor

We add multi columns support for editor,
now you can add columns to your document.
Works with export.
📄AGPL feature.

src/frontend/apps/e2e/__tests__/app-impress/doc-export.spec.ts

@@ -346,4 +346,69 @@ test.describe('Doc Export', () => {
     const pdfData = await pdf(pdfBuffer);
     expect(pdfData.text).toContain('Hello World');
   });
+
+  test('it exports the doc with multi columns', async ({
+    page,
+    browserName,
+  }) => {
+    const [randomDoc] = await createDoc(
+      page,
+      'doc-multi-columns',
+      browserName,
+      1,
+    );
+
+    await page.locator('.bn-block-outer').last().fill('/');
+
+    await page.getByText('Three Columns', { exact: true }).click();
+
+    await page.locator('.bn-block-column').first().fill('Column 1');
+    await page.locator('.bn-block-column').nth(1).fill('Column 2');
+    await page.locator('.bn-block-column').last().fill('Column 3');
+
+    expect(await page.locator('.bn-block-column').count()).toBe(3);
+    await expect(
+      page.locator('.bn-block-column[data-node-type="column"]').first(),
+    ).toHaveText('Column 1');
+    await expect(
+      page.locator('.bn-block-column[data-node-type="column"]').nth(1),
+    ).toHaveText('Column 2');
+    await expect(
+      page.locator('.bn-block-column[data-node-type="column"]').last(),
+    ).toHaveText('Column 3');
+
+    await page
+      .getByRole('button', {
+        name: 'download',
+        exact: true,
+      })
+      .click();
+
+    await expect(
+      page.getByRole('button', {
+        name: 'Download',
+        exact: true,
+      }),
+    ).toBeVisible();
+
+    const downloadPromise = page.waitForEvent('download', (download) => {
+      return download.suggestedFilename().includes(`${randomDoc}.pdf`);
+    });
+
+    void page
+      .getByRole('button', {
+        name: 'Download',
+        exact: true,
+      })
+      .click();
+
+    const download = await downloadPromise;
+    expect(download.suggestedFilename()).toBe(`${randomDoc}.pdf`);
+
+    const pdfBuffer = await cs.toBuffer(await download.createReadStream());
+    const pdfData = await pdf(pdfBuffer);
+    expect(pdfData.text).toContain('Column 1');
+    expect(pdfData.text).toContain('Column 2');
+    expect(pdfData.text).toContain('Column 3');
+  });
 });