feat(tauri): proactive update notifications via toast (P5-40)

TauriUpdateFeature component in ClientNonUIFeatures checks for updates
on mount and every 12h (skips if checked within the window). On update
available, fires a Lotus toast: "Lotus Chat vX.Y.Z is ready to install."
Clicking the toast calls install(). No-op on web (isTauri guard).

Also adds optional onClick to ToastNotif type and wires it in
LotusToastContainer so custom click handlers can skip hash navigation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/toast/LotusToastContainer.tsx

@@ -41,8 +41,12 @@ function ToastCard({ toast }: ToastCardProps) {
   }, [dismiss, toast.id]);
 
   const handleCardClick = () => {
-    // window.location.hash setter auto-prepends '#', so values must not include it
-    window.location.hash = toast.hashPath ?? `/room/${toast.roomId}`;
+    if (toast.onClick) {
+      toast.onClick();
+    } else {
+      // window.location.hash setter auto-prepends '#', so values must not include it
+      window.location.hash = toast.hashPath ?? `/room/${toast.roomId}`;
+    }
     dismiss(toast.id);
   };