Introduces a "Display sections as" picker in Home settings with List and
Grid modes. Grid renders each section as a horizontal shelf of video
cards, defaulting to Grid on tvOS and List on iOS/macOS. Per-platform
defaults are preserved via a platform-specific settings key.
On tvOS the shelf is a focus section so swiping up/down between rows of
different lengths works without getting stuck at the end of a row.
Remove 32 non-dotted keys (16 unused format specifiers, 16 word keys)
and replace with properly namespaced dotted keys following the existing
convention (common.*, player.*, search.*).
