feat: add notification sounds (#44)

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### Tests

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Reviewed-on: #44
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src-tauri/src/config.rs

@@ -46,6 +46,12 @@ pub struct HikariConfig {
 
     #[serde(default)]
     pub greeting_custom_prompt: Option<String>,
+
+    #[serde(default = "default_notifications_enabled")]
+    pub notifications_enabled: bool,
+
+    #[serde(default = "default_notification_volume")]
+    pub notification_volume: f32,
 }
 
 impl Default for HikariConfig {
@@ -59,6 +65,8 @@ impl Default for HikariConfig {
             theme: Theme::default(),
             greeting_enabled: true,
             greeting_custom_prompt: None,
+            notifications_enabled: true,
+            notification_volume: 0.7,
         }
     }
 }
@@ -67,6 +75,14 @@ fn default_greeting_enabled() -> bool {
     true
 }
 
+fn default_notifications_enabled() -> bool {
+    true
+}
+
+fn default_notification_volume() -> f32 {
+    0.7
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
 #[serde(rename_all = "lowercase")]
 pub enum Theme {
@@ -103,6 +119,8 @@ mod tests {
             theme: Theme::Light,
             greeting_enabled: true,
             greeting_custom_prompt: Some("Hello!".to_string()),
+            notifications_enabled: true,
+            notification_volume: 0.7,
         };
 
         let json = serde_json::to_string(&config).unwrap();