Fix chat layout height under messages tab

Summary

The chat layout height under the messages tab is broken, requiring scrolling on mobile when it should fit the screen.

Steps to Reproduce

1. Open the messages tab on mobile.
2. Observe the chat layout height.

Expected Behaviour

The chat layout should fit the screen without requiring scrolling, similar to the Snek app.

Actual Behaviour

The chat layout height is broken, and scrolling is necessary on mobile.

Environment

Not provided.

Reported by retoor via DevPlace.