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/assets/3d/load3d_node.json

@@ -0,0 +1,47 @@
+{
+  "last_node_id": 1,
+  "last_link_id": 0,
+  "nodes": [
+    {
+      "id": 1,
+      "type": "Load3D",
+      "pos": [50, 50],
+      "size": [400, 650],
+      "flags": {},
+      "order": 0,
+      "mode": 0,
+      "inputs": [],
+      "outputs": [
+        {
+          "name": "IMAGE",
+          "type": "IMAGE",
+          "links": null
+        },
+        {
+          "name": "MASK",
+          "type": "MASK",
+          "links": null
+        },
+        {
+          "name": "MESH",
+          "type": "MESH",
+          "links": null
+        }
+      ],
+      "properties": {
+        "Node name for S&R": "Load3D"
+      },
+      "widgets_values": ["", 1024, 1024, "#000000"]
+    }
+  ],
+  "links": [],
+  "groups": [],
+  "config": {},
+  "extra": {
+    "ds": {
+      "offset": [0, 0],
+      "scale": 1
+    }
+  },
+  "version": 0.4
+}