Fix chat layout height under messages tab

Summary

The chat layout height under the messages tab is broken. It works on mobile but requires scrolling. The layout should fit the screen without scrolling.

Steps to Reproduce

Not provided.

Expected Behaviour

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

Actual Behaviour

The chat layout height is broken; on mobile it works but requires scrolling.

Environment

Not provided.

Reported by retoor via DevPlace.