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.

packages/i18n/locales/en/auth.json

@@ -51,9 +51,9 @@
     "copy_server": "Copy the server address",
     "step_updates": {
       "android": "Sign in with your account. The app offers new versions by itself.",
-      "windows": "Sign in with your account. Get a new version from this page.",
-      "linux": "Sign in with your account. Get a new version from this page.",
-      "macos": "Sign in with your account. Get a new version from this page."
+      "windows": "Sign in with your account. The app will offer new versions.",
+      "linux": "Sign in with your account. The app will offer new versions through your system package installer.",
+      "macos": "Sign in with your account. The app will offer new versions."
     },
     "checksum": "SHA-256 checksum",
     "unavailable": "Apps are not available yet: release downloads are not configured on this server (docs/deployment.md).",