feat(desktop): add offline cache and verified app updates

Clean release notes in Android and desktop update dialogs. Persist downloaded audio and offline playback events per server and user; add desktop update checks, checksum verification and installer launch.

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

@@ -1,6 +1,7 @@
 mod media;
 mod proxy;
 mod store;
+mod update;
 
 use media::Media;
 use proxy::Proxy;
@@ -110,6 +111,7 @@ pub fn run() {
     tauri::Builder::default()
         .plugin(tauri_plugin_single_instance::init(|app, _, _| show_main(app)))
         .plugin(tauri_plugin_window_state::Builder::default().build())
+        .manage(update::Updater::default())
         .setup(|app| {
             let saved = store::load_server(app.handle())?;
             let proxy = tauri::async_runtime::block_on(Proxy::start(saved.clone())).map_err(|e| e.to_string())?;
@@ -150,7 +152,8 @@ pub fn run() {
             Ok(())
         })
         .invoke_handler(tauri::generate_handler![
-            bootstrap, set_server, clear_server, token_get, token_set, token_clear, user_get, user_set, user_clear, media_set
+            bootstrap, set_server, clear_server, token_get, token_set, token_clear, user_get, user_set, user_clear, media_set,
+            update::update_check, update::update_install
         ])
         .run(tauri::generate_context!())
         .expect("desktop app failed to start");