feat(desktop): implement media extraction engine, sys integrations, and UI polish

- Implement get_free_space and set_prevent_sleep in Rust backend
- Add robust media extraction UI and format parser in AddDownloadsModal.tsx
- Wire application settings to Zustand store
- Add global user-select: none for native text feel
- Fix window dragging in Sidebar.tsx
- Add GitHub Actions CI workflow for Tauri cross-platform build

apps/desktop/src/index.css

@@ -113,6 +113,11 @@
     transition: background-color 0.3s cubic-bezier(0.4, 0, 0.2, 1), color 0.3s cubic-bezier(0.4, 0, 0.2, 1);
   }
 
+  * {
+    user-select: none;
+    -webkit-user-select: none;
+  }
+
   input, textarea {
     user-select: auto;
     -webkit-user-select: auto;