Support pasting images from clipboard into the conversation

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

Support pasting images from clipboard into the conversation

### Proposed solution

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

Support pasting images from clipboard into the conversation

### Proposed solution

Allow users to paste images (e.g., screenshots) directly into the CLI input using Ctrl+V / Cmd+V. The image would be sent as a vision-capable attachment to the model, similar to how @
mentions include file contents. The CLI could display a small inline preview or placeholder like [📷 Image pasted from clipboard] before sending. For terminals that don't support inline images, just
showing the placeholder text is fine — the image data would still be sent to the model.

### Example prompts or workflows

1. User takes a screenshot of a UI bug → pastes into CLI → asks "What's wrong with this layout?" — the model analyzes the screenshot and suggests CSS/HTML fixes.
2. User pastes a screenshot of an error dialog from a mobile emulator → asks "Fix this error" — no need to manually transcribe the error message.
3. User pastes a design mockup → asks "Implement this component using Tailwind CSS" — the model generates code matching the visual reference.
4. User pastes a screenshot of terminal output that's hard to copy as text (e.g., from a remote machine or a Docker log viewer) → asks "What does this error mean?"

### Additional context

Currently, sharing visual context requires either taking a screenshot via Chrome DevTools integration (only works for browser pages) or saving an image to a file and referencing it with
@. Clipboard pasting is a much faster workflow — especially for UI/UX work, debugging visual issues, or when the user wants to show something from outside the terminal (design tools, browser, mobile
emulators). Most AI chat interfaces (ChatGPT, Claude web) already support this, and bringing it to the CLI would significantly reduce friction for visual debugging workflows.

Reopening the issue @examon @andyfeller https://github.com/github/copilot-cli/issues/2409

As I explained there, the current behavior for Mac, at least, using the screenshot tool (command+shift+4) and copying to clipboard and pasting in the CLI does not work.

### Example prompts or workflows

_No response_

### Additional context

_No response_

首先追蹤 CLI 輸入路徑以及現有的 @-mention 檔案附件流程，該 issue 將其確定為最接近的比較對象。將完成定義為：接受 Ctrl+V/Cmd+V 貼上的影像資料，將其作為支援 vision 的附件傳送，並在終端無法內嵌顯示影像時顯示佔位符。

由索引模型根據 Issue 內容生成。