Feat: background head-preload for sample libraries

src/state/audio.rs

@@ -223,6 +223,7 @@ pub struct AudioSettings {
     pub input_list: ListSelectState,
     pub restart_pending: bool,
     pub error: Option<String>,
+    pub sample_registry: Option<std::sync::Arc<doux::SampleRegistry>>,
 }
 
 impl Default for AudioSettings {
@@ -244,6 +245,7 @@ impl Default for AudioSettings {
             },
             restart_pending: false,
             error: None,
+            sample_registry: None,
         }
     }
 }