Slow UI performance on linux

**Describe the bug**
The UI is very sluggish on linux. Things such as the automatic highlighting style change after hovering a message can take a half second.

**Steps to reproduce**
1. Open the app
2. Get an agent to start working on something
3. Scroll
4. Notice it takes significant time before scrolling happens
**Expected behavior**
What did you expect to happen?

**Version and platform**
Find your version at the bottom of the Settings sidebar. Write "unknown" if you can't determine it.
- Buzz version: v0.4.26
- OS: Linux Mint

**Logs / additional context**
Seems to be affected by whether or not an agent is running (worse when agent running)

Start by reproducing the sluggish scrolling and delayed hover highlighting on Linux Mint with Buzz v0.4.26, both with and without an agent running, as described in the issue. Trace the UI path involved in scrolling and message hover updates; done means the reported delays are resolved or measurably reduced under those conditions.

Written by the indexing model from the issue text.