fix: use Tauri clipboard plugin for reliable share links

- Add tauri-plugin-clipboard-manager for reliable clipboard access
- Replace browser clipboard API with Tauri plugin
- Improve error messages in share functions to be more specific
- Add loading indicator for Song.link fetch

package.json

@@ -14,6 +14,7 @@
   "license": "MIT",
   "dependencies": {
     "@tauri-apps/api": "^2",
+    "@tauri-apps/plugin-clipboard-manager": "^2",
     "@tauri-apps/plugin-dialog": "^2.5.0",
     "@tauri-apps/plugin-opener": "^2",
     "lucide-svelte": "^0.562.0",