Plain-Form sheets rendered as columns-style content floating inside
oversized fixed frames on macOS. Anchor these panels to their toolbar
buttons as popovers instead, sized to content; iOS/tvOS keep sheets.
- Search and PeerTube explore filters apply live (Cancel never
reverted anything anyway) and dismiss on outside click
- Subscriptions/Manage Channels "Subscriptions Data" opens as a sheet
from the popover's onDisappear via a pending flag, since presenting
while the popover dismisses gets swallowed
- Media browser view options drop navigation chrome on macOS
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