style(ui): redesign app layout to native macOS density and refine visual theme

- Adjusted overall layout scale to perfectly match original native macOS density.

- Refined sidebar into a floating rounded slab with proper padding, border, and toggle button placement.

- Fixed drag region overlap preventing button interactions in the title bar.

- Removed artificial shadow lines and scrollbars from the sidebar.

- Updated Tauri backend configuration, dependencies, and scheduler functions for improved stability.

apps/desktop/src-tauri/src/scheduler.rs

@@ -20,7 +20,7 @@ struct SchedulerSettings {
 }
 
 pub fn spawn_scheduler(app_handle: tauri::AppHandle) {
-    tokio::spawn(async move {
+    tauri::async_runtime::spawn(async move {
         let mut interval = tokio::time::interval(Duration::from_secs(10));
         loop {
             interval.tick().await;