Support pasting images from the system clipboard into copilot CLI prompts

### Describe the feature or problem you'd like to solve

Support pasting images from the system clipboard into copilot CLI prompts

### Proposed solution

When using Copilot CLI with image-based prompts (e.g., screenshots of code, UI bugs, logs),
there is currently no way to paste an image directly from the system clipboard.

Instead, users must:
1. Save the image to disk
2. Remember the file location
3. Paste the file path into the CLI

This adds unnecessary friction for a very common workflow, especially when iterating
quickly on screenshots or transient images.

This aligns Copilot CLI with modern multimodal workflows already supported
in IDEs and chat UIs, and would make the CLI a first-class interface rather
than a fallback.

### Example prompts or workflows

_No response_

### Additional context

_No response_