Improve large Copy/Paste text

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

Display first 1 or 2 lines whenc "Copy paste"

### Proposed solution

It'd be helpfull if Copilot CLi could show the first 1 or 2 lines when pasting large texts, so rather than

```
[Paste #1 - 133 lines]
```

show this:

```
Please generate a Monday report....
[Paste #1 - 132 lines]
```

### Example prompts or workflows

_No response_

### Additional context

_No response_

Start by locating the Copy/Paste handling that formats large pasted text, then reproduce the behavior with a multiline input. Done means large pastes show their first one or two lines before the paste marker, with the displayed line count adjusted consistently.

Written by the indexing model from the issue text.