Feat: demo songs

src/settings.rs

@@ -58,6 +58,10 @@ pub struct DisplaySettings {
     pub hue_rotation: f32,
     #[serde(default)]
     pub onboarding_dismissed: Vec<String>,
+    #[serde(default = "default_true")]
+    pub load_demo_on_startup: bool,
+    #[serde(default)]
+    pub demo_index: usize,
 }
 
 fn default_font() -> String {
@@ -105,6 +109,8 @@ impl Default for DisplaySettings {
             layout: MainLayout::default(),
             hue_rotation: 0.0,
             onboarding_dismissed: Vec::new(),
+            load_demo_on_startup: true,
+            demo_index: 0,
         }
     }
 }