appview: pages: refactor base layout to be one big grid so we can avoid min-h-screen workarounds that cause permanent scrolling #359

this is great! thanks for the submission. couple of changes:

• topbar has mb-4 which can be removed now that body has gap-4
• in commit/patch/compare/interdiff views, could we use col-span-full as opposed to col-span-1 md:col-span-12?

both seemed reasonable to me! changed the mt-16 on footer to mt-12 as well to account for the gap-4 there too

i also noticed that the footer has rounded-t while the header has rounded. would probably make sense to change that to a rounded-b to match the footer. idk if thats straying off the point of this PR stack a bit though? might make better sense in a later PR or as just a plain commit. (its not like i dont also have more things i want to change here eventually so. like the semantic HTML stuff and eventually refactoring commit/patch/compare/interdiff out so they all use a combined "wide layout" base or something of the sort)