Patch/UI test dom assertions

[psilabs-dev]

Apply these fixes with playwright tests.

1. in a normal stable page, there shouldn't be a spinner anywhere.
2. in a normal UI page, there should be no error toasts.
3. any playwright test needs user actions instead of API calls when testing any UI scope of interest (automation is exempt unless what's being automated is the thing being tested, in which case -> run test with user actions).

DX improvement: PlaywrightTestContextManager to manage every single playwright context. Without it, logic errors and scope coverage leaks are happening all over the place, it's getting kind of ridiculous also how often duplication is happening.