Give TVSidebarDetailContainer an optional bottom action slot and use it to
show the Add Source button beside the sources list on tvOS. Switch the
Settings > Sources list from a focus-capturing List to the same
ScrollView+LazyVStack layout MediaSourcesView already uses, drop
.buttonStyle(.card) so row icons no longer clip, and bump the row
icon-to-title spacing to 24pt. Replace the sheet-based Add/Edit flow in
MediaSourcesView with navigationDestinations wrapped in the sidebar
container, and decorate each Add Source form (WebDAV, SMB, remote server,
PeerTube browse) with its own sidebar icon and title.
- Replace sheets with navigationDestination for Add/Edit Source on tvOS
(tvOS sheets have fixed size that doesn't fit the content)
- Fix focused cell clipping by replacing TVSettingsContainer's frame-based
layout with safeAreaInset, matching the main settings view pattern
- Use standard List with .listStyle(.grouped) for Sources on tvOS
- Add sidebar icons and titles to TVSettingsContainer for all settings
subviews, utilizing the left column space
- Remove redundant large navigation titles on tvOS (shown in sidebar)
- Move Edit Source Save button from toolbar into form above Delete button
for better tvOS focus navigation
