Holding Ctrl+V pastes the same image repeatedly (no debounce/repeat guard)

### Description
When pasting an image into the chat input, holding down `Ctrl+V` fires the paste event continuously with no debounce or key-repeat guard. Holding it for ~10 seconds inserts ~100 copies of the same image into the conversation.

### Version
GitHub Copilot CLI 1.0.69-0 (desktop)

### OS
Windows

### Steps to reproduce
1. Copy an image to the clipboard.
2. Focus the chat input.
3. Press and hold `Ctrl+V` for several seconds.

### Expected behavior
A held `Ctrl+V` should paste the image once (or be debounced / ignore key auto-repeat), like a normal single paste.

### Actual behavior
The image is pasted repeatedly (one insert per key-repeat event), flooding the chat with dozens of duplicate images.

Start at the chat input's image-paste handling and reproduce the issue on Windows by holding Ctrl+V with an image on the clipboard. Trace how repeated paste events are processed, then verify that one held keypress inserts only one image and that normal separate pastes still work.

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