Dark tone setting: grey Dark (default) vs near-black Darker

Tone row appears under Theme when the effective theme is dark.
Grey palette uses macOS-like #26262a background.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/shared/types.ts

@@ -64,6 +64,8 @@ export type AccentTone =
 
 export interface AppSettings {
 	theme: "system" | "light" | "dark";
+	/** Dark appearance: grey ("dark") or near-black AMOLED ("darker"). */
+	darkTone: "dark" | "darker";
 	/** Accent tone for chrome and selection tint; graphite = neutral zinc. */
 	accent: AccentTone;
 	/** File-list icons: plain neutral glyphs, or per-category glyphs and colors. */
@@ -85,6 +87,7 @@ export interface AppSettings {
 
 export const DEFAULT_SETTINGS: AppSettings = {
 	theme: "system",
+	darkTone: "dark",
 	accent: "blue",
 	iconColors: "multi",
 	speedUnit: "MBps",