Image ALT texts are sometimes displayed, sometimes hidden behind "ALT" button

THANKS FOR AN AMAZING PROJECT :heart:

**Describe the bug**

I'm wondering why sometimes image alt texts are visible and other times there's an "alt" button that needs to be clicked.

I cannot find a consistent pattern.

**To Reproduce**

ALT button: `https://fosstodon.org/@mariatta/112441181927547930` :disappointed:

ALT text as caption: `https://fosstodon.org/@mariatta/112426998242061472` :partying_face:

**Expected behavior**

I would like for ALT texts to always display. It's nice and encourages more usage. See also this blog post that praises Phanpy stats: https://stefanbohacek.com/blog/impact-of-fediverse-clients-on-the-use-of-alt-text/

Compare the two referenced Mastodon posts to reproduce the differing image ALT behavior, then trace the frontend image-rendering entry point that determines whether text is shown or placed behind the ALT button. Done means image ALT text is consistently displayed for both cases; the issue does not name a file or test to run.

Written by the indexing model from the issue text.