test: add basic E2E tests for Load3D node (#10731)

## Summary
Add Playwright tests covering widget rendering, controls menu
interaction, background color change, and recording controls visibility.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10731-test-add-basic-E2E-tests-for-Load3D-node-3336d73d36508194bff9eb2a7c9356b9)
by [Unito](https://www.unito.io)

browser_tests/tests/load3d/Load3DHelper.ts

@@ -0,0 +1,40 @@
+import type { Locator } from '@playwright/test'
+
+export class Load3DHelper {
+  constructor(readonly node: Locator) {}
+
+  get canvas(): Locator {
+    return this.node.locator('canvas')
+  }
+
+  get menuButton(): Locator {
+    return this.node.getByRole('button', { name: /show menu/i })
+  }
+
+  get recordingButton(): Locator {
+    return this.node.getByRole('button', { name: /start recording/i })
+  }
+
+  get colorInput(): Locator {
+    return this.node.locator('input[type="color"]')
+  }
+
+  getUploadButton(label: string): Locator {
+    return this.node.getByText(label)
+  }
+
+  getMenuCategory(name: string): Locator {
+    return this.node.getByText(name, { exact: true })
+  }
+
+  async openMenu(): Promise<void> {
+    await this.menuButton.click()
+  }
+
+  async setBackgroundColor(hex: string): Promise<void> {
+    await this.colorInput.evaluate((el, value) => {
+      ;(el as HTMLInputElement).value = value
+      el.dispatchEvent(new Event('input', { bubbles: true }))
+    }, hex)
+  }
+}