feat(settings): add folder selection for music and playlists

Add UI and logic to select music and playlists folders in settings using
tauri dialog plugin. Integrate @tauri-apps/plugin-dialog, plugin-fs, and
plugin-store in both frontend and backend. Update capabilities and
dependencies to support new plugins. Improve settings page with folder
selectors and info note for better user experience.

src-tauri/Cargo.toml

@@ -20,6 +20,9 @@ tauri-build = { version = "2", features = [] }
 [dependencies]
 tauri = { version = "2", features = [] }
 tauri-plugin-opener = "2"
+tauri-plugin-store = "2"
+tauri-plugin-dialog = "2"
+tauri-plugin-fs = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"