[UX]: Resize chat input field based on content

[jvstme]

Current

In the model chat, the input field can only fit 3 lines of text. Working with longer messages is inconvenient, as it requires scrolling.

The "System" field also cannot fit much text unless resized manually.

Proposed

Adjust both fields' height automatically based on content, the same way as in common messaging apps. Forbid resizing manually.

[github-actions]

This issue is stale because it has been open for 30 days with no activity.

[olgenn]

Completed in #1825