A quieter interface

No new features this round. The existing ones get sharper.

• The compact sidebar now explains itself with tooltips
• Lists and command palettes fade at the edges as you scroll
• The mobile bottom nav always shows where you are
• Pinned podcasts now show their covers
• Paste a feed URL directly into Discover
• Links to other sites open in your system browser on desktop
• Feeds that fall behind catch up on their own