Implement Vue-based spinner for image upload in Nodes 2.0 mode

## Context

Currently, PR #9189 implements a canvas-based loading spinner for image uploads in LoadImage nodes. However, when `vueNodesMode` is enabled, `drawNode` skips all canvas rendering (LGraphCanvas line 5396-5403), making the spinner invisible in Nodes 2.0.

## Task

Implement a Vue-based spinner for the image preview overlay that works with Nodes 2.0 compatibility.

## References

- PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/9189
- Comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/9189#discussion_r2856396701
- Requested by: @christian-byrne

## Implementation Notes

The Vue-based spinner should:
- Display during image upload operations
- Be visible when vueNodesMode is enabled
- Integrate with the existing image preview overlay component
- Maintain consistency with the current upload UX (filename updates, etc.)

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