Description

Closes #169

Originally, both the sidebar and its background were part of the same AnimatedVisibility block, causing them to move and fade together. This is resolved by animating the background independently, using animateFloatAsState to control the alpha value of the background Box.

Checklist

• I have read the contribution guidelines: https://github.com/permissionlesstech/bitchat-android?tab=readme-ov-file#contributing
• I have performed a self-review of my code

• I have mentioned the corresponding issue and the relevant keyword (e.g., "Closes: #xy") in the description (see https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue)
• If it is a core feature, I have added automated tests

Fix: