feat: Introduce reader settings and dark mode support

Adds a new `ReaderSettings` type to manage user preferences such as dark mode, font size, line height, font family, and auto-scroll behavior.

Implements dark mode styling for various UI components including the `VoiceSelector` and `QueueItem`, enhancing visual consistency.

Enhances the `ReaderView` component to respect the `autoScroll` setting and introduces basic text styling options based on the new settings.

types.ts

@@ -45,3 +45,11 @@ export interface PlayerState {
   currentArticleId: string | null;
   selectedVoice: VoiceName;
 }
+
+export interface ReaderSettings {
+  isDarkMode: boolean;
+  fontSize: 'sm' | 'base' | 'lg' | 'xl' | '2xl';
+  lineHeight: 'normal' | 'relaxed' | 'loose';
+  fontFamily: 'sans' | 'serif' | 'mono';
+  autoScroll: boolean;
+}