Disable zoom on custom pages

[tfuxu]

~~Instead of globally storing zoom level, it should be stored by each webview page (and it should be disabled completely in custom pages, eg. input page)~~

We should disable zoom controls on custom pages (eg. user input page), as they can't be (easily, if at all) resized.

[ranfdev]

I'm ok with disabling the zoom on the custom pages, like the input one, but it doesn't make much sense to have a separate zoom for each gemini page.

HTML browsers have different zoom levels for each page because each website has a custom font size. Here the font size is the same everywhere. Why would a user zoom page X but not page Y when the formatting is the same?

[tfuxu]

I agree, I've updated title and issue description to focus it only on disabling zoom in custom pages.