Simplify/Reclarify "Impossible to Identify" pop-up on observation upload

[bouteloua]

@silversea_starsong

My main gripe right now is more that when I have a long list of obs, and I can’t find the one that’s missing details quickly. A red highlight box around the “trouble” obs could help a lot too.

Linking related request for future reference: https://forum.inaturalist.org/t/missing-something-pop-ups-in-web-uploader-should-also-highlight-observations-that-triggered-them/30373