System color mode preference

Follow the operating system's color mode, save the selected preference, and get fixes for Select highlighting and Table empty states.

New features

• Added "system" to defaultColorMode on VortexProvider and setColorMode on useTheme to follow operating system appearance changes. Selecting "light" or "dark" stops following the system.
• Added onColorModePreferenceChange to VortexProvider, colorModePreference to useTheme, and the exported ColorModePreference type to read and persist the preference, including "system".

Bug fixes

• Fixed Select highlighting for items passed from server components and items that finish loading after suspending.
• Fixed Table empty states appearing behind pinned columns.