some small ui tweaks

Created by: ShittyKopper

• rounded timeline corners when "Show a gap between posts on the timeline" is disabled
• show a pointer cursor when hovering over clickable parts of notes when "Click to open notes" is enabled
• hide status indicators when they're in an "unknown" state
• add more shadows

before

after

there are three parts of this pr i'm not too sure on:

• i directly copied the ._shadow helper's box-shadow definition for consistency, but i'm not entirely sure if the size of those shadows fit the ui. it may make sense to play with the individual shadow sizes
  • imo it's still better than having no separation between the elements and the background
• 4fcd47bf087480b3ee731eff4d24f5de2b40fe29 feels a bit too "fragile" as i just apply a shadow to all panel elements no matter what. so far there is only one obvious exception i could find that needed reverting (notifications), but there's probably more out there i haven't encountered. unsure about that commit.
  • that said, individually hunting down parts that could use a shadow in a codebase as large as misskey feels like a tiring job, so not sure on what the best way to approach that would be
• pnpm lint runs out of memory in my laptop