Pipe characters (`|`) are copied when selecting prompt text

[stagefright5]

When selecting and copying prompt text from the CLI input box, the | border characters are also included in the clipboard content.

Steps to Reproduce:

1. Add a multiline prompt in the input box of gemini cli
2. Use mouse to select the prompt

Expected Behavior:

Only the actual prompt text should be copied, without the decorative border characters.

Actual Behavior:

The | pipe characters used for visual borders are included in the copied text.

Example:

• The prompt in the cli

• The Copied Text

│ > Please follow the rules:                                                                                                                                                           │
│   - Always use signals API for state management                                                                                                                                      │
│   - Don't use decorator based Inputs and Outputs                                                                                                                                     │
│   - Always create `standalone` components