Document when `prevent_default()` deviates from web expectations

Just spent a while debugging a form submission issue because I was using `evt.prevent_default()` with a web mindset (the submit button will

This seems to have caused confusion for others in the past as well:
https://github.com/DioxusLabs/dioxus/issues/4045#issuecomment-2832226129
https://github.com/DioxusLabs/dioxus/issues/3904#issuecomment-2751486202
https://github.com/DioxusLabs/dioxus/issues/1297

I get that for cross-platform support the deviation makes sense, but since the Dioxus docs reference the MDN docs so much, I think it makes sense to have an explicit call-out for this.

I made the issue title focused on this specific deviation from expectations, but if there are other cases (web, desktop, or otherwise) it could make sense to have a page dedicated to framework design decisions that may conflict with preconceived notions from past experience. I'd imagine it would help with quicker acclimation for people coming from other frameworks.