feat: Add settings to control play button visibility on home shelves

This commit introduces new functionality to customize the visibility of the
play button on home page shelves.

Key changes:

- Added `HomePageSettings` to `AppSettings` to store your preferences:
    - `showPlayButtonOnContinueShelves`: Controls visibility on "Continue Listening" and "Continue Series" shelves (default: true).
    - `showPlayButtonOnAllShelves`: Controls visibility on other shelves (default: false).
- Modified `BookHomeShelf` to respect these settings when rendering books.
- Created a new "Home Page Settings" page under "Appearance" in App Settings, allowing you to toggle these two options.
- Added comprehensive unit and widget tests to cover the new settings model, the conditional logic in `BookHomeShelf`, and the functionality of the new settings page.

lib/settings/models/app_settings.dart

@@ -19,12 +19,24 @@ class AppSettings with _$AppSettings {
     @Default(NotificationSettings()) NotificationSettings notificationSettings,
     @Default(ShakeDetectionSettings())
     ShakeDetectionSettings shakeDetectionSettings,
+    @Default(HomePageSettings()) HomePageSettings homePageSettings,
   }) = _AppSettings;
 
   factory AppSettings.fromJson(Map<String, dynamic> json) =>
       _$AppSettingsFromJson(json);
 }
 
+@freezed
+class HomePageSettings with _$HomePageSettings {
+  const factory HomePageSettings({
+    @Default(true) bool showPlayButtonOnContinueShelves,
+    @Default(false) bool showPlayButtonOnAllShelves,
+  }) = _HomePageSettings;
+
+  factory HomePageSettings.fromJson(Map<String, dynamic> json) =>
+      _$HomePageSettingsFromJson(json);
+}
+
 @freezed
 class ThemeSettings with _$ThemeSettings {
   const factory ThemeSettings({