Better playwright tests

I really struggle writing good playwright tests ... I find that stuff that works locally fails on Github's CI, and I haven't dug in to try to figure out why (e.g. https://github.com/developmentseed/stac-map/pull/161/commits/7d7d8bd0de51416b15431ce4f073bfea6cbf5432). I'd love to be able to assert more stuff about our app, but kind of need some help.