[Bug]Copying commands from copilot cli includes invisible characters, causing "command not found" in external terminal

### Describe the bug

# Bug: Copying commands from code blocks includes invisible characters, causing "command not found" in external terminal

## Description

When copying commands from Copilot CLI's rendered code blocks (using `ctrl+c` or right-click copy) and pasting them into another terminal tab, the pasted text contains invisible/hidden characters. This causes valid system commands like `df` and `du` to fail with "command not found", even though the commands appear visually correct.

Manually deleting the pasted text with Backspace and retyping the exact same command works perfectly.

## Steps to Reproduce

1. Launch Copilot CLI (`copilot`) in a terminal tab (e.g., Windows Terminal + WSL)
2. Ask: "give me a linux command, calc the disk size"
3. Copilot responds with commands including `df -h` and `du -sh .` in code blocks
4. Select and copy `df -h` from the code block (ctrl+c / right-click copy)
5. Switch to a **separate** terminal tab (same WSL instance)
6. Paste the command and press Enter

## Expected Behavior

`df -h` should execute normally and display filesystem disk usage.

## Actual Behavior

```
$ df -h
Command 'df' not found, did you mean:
command 'wdf' from deb wit (3.01a-4.1)
command 'df' from deb coreutils (9.4-3ubuntu6.2)
command 'kdf' from deb kdf (4:23.08.4-0ubuntu1)
command 'sdf' from deb sdf (2.001+1-9)
Try: sudo apt install
```

The same error occurs consistently when pasting. However, **pressing Backspace to delete the entire line and manually retyping `df -h` succeeds immediately**:

```
$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sdd 1007G 9.3G 947G 1% /
C:\ 952G 196G 757G 21% /mnt/c
...
```

This also reproduces with `du -sh .` and `du -sh /path/to/dir` copied from the code blocks — same "command not found" error on paste, works fine when manually typed.

## Additional Testing

Further manual testing confirms there is exactly **one invisible character prepended** before the visible command text:

1. After pasting `df -h`, move the cursor to the beginning of the line (Home key)
2. Press Right arrow once to move past the first "visible" character `d`
3. Press Backspace once to delete `d`, then retype `d` to restore the command → **still fails**
4. Move cursor to the beginning again, press Backspace **twice** (deleting both the invisible character and `d`), then retype `d` to restore the command → **succeeds**

This proves there is a **single hidden/non-printable character at the very beginning** of the copied text, before the first visible character. Deleting only the visible `d` and retyping it leaves the hidden character intact, so the command still fails. Deleting one extra character removes the hidden prefix, and the command works.

## Root Cause Hypothesis

The copied text from Copilot CLI code blocks contains exactly one invisible Unicode character (e.g., zero-width space U+200B, BOM U+FEFF, or other non-printable character) **prepended before the command text**. This character is part of the terminal rendering but should be stripped when copying to clipboard.

## Environment

- **Copilot CLI version**: 1.0.11
- **OS**: Ubuntu 24.04.4 LTS (WSL2)
- **Kernel**: 6.6.87.2-microsoft-standard-WSL2 (aarch64)
- **Terminal**: Windows Terminal
- **Shell**: Bash

## Video Evidence

A screen recording demonstrating the issue is available. Key observations:
- The bug is **100% reproducible** with paste
- The bug is **100% resolved** by Backspace + manual retype
- Both `df` and `du` are affected (not command-specific)
- Using Up arrow to recall the pasted command from history also fails (invisible characters persist in bash history)

https://github.com/user-attachments/assets/889447ee-0c0e-4647-b8bb-5cdd3a723bed

### Affected version

_No response_

### Steps to reproduce the behavior

_No response_

### Expected behavior

_No response_

### Additional context

_No response_