Made transitions between screens consistent

[tashilapathum]

I noticed when opening a book from the list, there's a fade in animation, when closing it, the animation is zoom out but sometimes it just fades out if done immediately.

screen-20260102-172108-1767354649191.mp4

Those are the default nav 3 animations and it looks janky. So I added transitionSpecs to make them consistent across all screens. I experimented with different transitions but settled in on simply fade in and out. Now it's like this:

screen-20260102-172146-1767354689030.mp4

PS: I've been using this app for years for my audiobooks and it's the absolute best. Thank you for the amazing work.

[tashilapathum]

This also fixes issue #3281

[tashilapathum]

Hi @PaulWoitaschek, any issue preventing this PR from being merged?