Group font_size no longer affects group title rendering since v0.21.1

### Custom Node Testing

- [x] I have tried disabling custom nodes and the issue persists (see [how to disable custom nodes](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled) if you need help)

### Expected Behavior

The group title should respect the configured `font_size` value.

For example, when `font_size` is set to `80`, the group title should be rendered in a large font, as it was in ComfyUI v0.20.3.

### Actual Behavior

The group `font_size` value is ignored in newer versions.

When I set the group `font_size` to `80`, the group title still renders with a small/default font size in v0.21.1 and later.

In v0.20.3, the same `font_size = 80` setting works correctly and the group title is displayed much larger.

I attached a comparison screenshot:
- Top: v0.20.3, `font_size = 80`, works correctly.
- Bottom: v0.21.1, `font_size = 80`, ignored.

### Steps to Reproduce

1. Open ComfyUI v0.21.1 or later.
2. Create a new group.
3. Set the group `font_size` to `80`.
4. Observe that the group title size does not change as expected.
5. Compare with ComfyUI v0.20.3 using the same group `font_size = 80`; the group title renders correctly with a large font.

### Debug Logs

```powershell
No crash or terminal error occurs.

Relevant environment information from startup log:

OS: Windows
ComfyUI version: v0.21.0
ComfyUI frontend version: 1.43.18
Python version: 3.11.6
PyTorch version: 2.7.0+cu128
xformers version: 0.0.30
GPU: NVIDIA GeForce RTX 5090
VRAM: 32607 MB
VRAM mode: NORMAL_VRAM

This appears to be a frontend/canvas rendering regression. The group font_size value is present in the workflow, but the group title is rendered with the default/small font size in v0.21.1 and later.
```

### Other

I attached a comparison screenshot.

The same workflow/group setting was tested in:
- ComfyUI v0.20.3: group `font_size = 80` works correctly.
- ComfyUI v0.21.1: group `font_size = 80` is ignored.

This appears to be a regression in the frontend/canvas group title rendering.