SettingsLayout lists sections down the side and shows the open one, the
list going above the page in a narrow box; SettingsSection and
SettingsRow title and hold settings, a row's control wrapping under its
name. SettingsSearch finds a setting by its name or words and opens its
section. ThemeSelector, AccentColorPicker, FontSizeControl and
DensitySelector set the look; KeyboardShortcutsList finds shortcuts by
every word; ProxySettings, PrivacySettings, NotificationSettings,
StartupSettings, StorageSettings with its clear, ImportExportSettings,
ResetToDefault, FeatureFlags and DeveloperModeToggle fill the rest.
Every handler a control needs is required and fails loud when missing.
ColorPalette wraps its swatches in a row capped at its columns, so it
keeps their size in a box sized by its content, and its swatches carry
the palette's id. ThemeSwitcher points here: src/theme sits under the
chapters that draw with buttons.
