Introduce PlatformMenuPicker that wraps short-option pickers in
LabeledContent + .pickerStyle(.menu) on tvOS so they render as a
compact dropdown instead of pushing a full-screen option list. On
iOS/macOS it falls through to a plain Picker, leaving rendering
unchanged.
Applied across Playback, Subtitles, Sidebar, Privacy, and Advanced
settings. Long language lists in PlaybackSettingsView are left as
push-style.
- 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
