[Bug] "Download All" button for missing models is unresponsive on Windows

## Description

When opening a workflow that requires missing models, the missing models panel correctly identifies the 3 missing files:
- `z_image_turbo_bf16.safetensors` (diffusion_models, 12.88 GB)
- `qwen_3_4b.safetensors` (text_encoders, 6.26 GB)
- `ae.safetensors` (vae, 0.13 GB)

However, clicking the **"全部下载 (Download All)"** button (19.27 GB total) does nothing — no download starts, no error message, no progress indicator.

Individual download buttons for each model are also unresponsive.

## Steps to Reproduce

1. Open a workflow that requires the above missing models
2. The missing models panel appears with the correct list
3. Click "全部下载 (Download All)" button
4. **Nothing happens** — no download, no error, no feedback

## Expected Behavior

Models should begin downloading with a progress indicator.

## Environment

- **OS:** Windows
- **ComfyUI:** Desktop version (latest)
- **UI Language:** Chinese (Simplified)

## Screenshot


> Note: Screenshot shows the missing models panel with 3 items and the unresponsive download button.