Delete declarations that Periphery reports unused on every platform that
compiles them (iOS, macOS, tvOS), including nine views used only by their
own previews. Platform-gated code still used on another platform, device-
only MPV render paths, migration models, CloudKit record names, App
Intents metadata and unused parameters are kept.
Sheet dismiss buttons rendered as an iOS-style circular glass "X" on
macOS 26, which looks foreign on the desktop. Add a shared
sheetCloseToolbarItem helper that renders a native text "Close" button
on macOS while keeping the compact icon-only xmark on iOS/tvOS, and
replace the ~14 duplicated inline close buttons across sheets with it.
Previously a failed video left the user staring at a black screen / thumbnail
with no indication anything went wrong — playbackState went to .failed but
TVPlayerView never read it. Add a focusable glass overlay (Details / Retry /
Play Next or Close) gated on isFailed and a parallel one for retry-exhausted
state, with the regular controls and background tap-target disabled while
either is visible so focus stays inside the overlay. Hide the Copy/Share
toolbar items in ErrorDetailsSheet on tvOS where they aren't useful.
