Adds an option in Appearance settings to use different accent colors
in light and dark mode, with a toggle to keep a single shared color
(the default, preserving existing behavior).
- New synced settings keys: accentColorDark, customAccentColorDark,
useSeparateDarkAccentColor; dark values fall back to the light
selection until explicitly set, so no migration is needed
- resolvedAccentColor returns a dynamic platform color (UIColor trait
provider / NSColor appearance provider) when the toggle is on, so
the root tint and all direct readers adapt to light/dark
automatically without consumer changes
- Accent Color section shows two stacked preset+custom grids with
Light/Dark headers when enabled, extracted into AccentColorGrid;
CustomAccentColorButton now takes bindings so the macOS color panel
edits whichever target was last opened
- New DarkAccentColorTests covering sync contract, default-off state,
fallbacks, and toggle-off resolution
Claude-Session: https://claude.ai/code/session_0154KH8RAVAvm6iVanhmoW8o
b632f11b2f