fix: forcing 3 sec for each notification instead of one replacing the other

frontend/src/App.tsx

@@ -490,11 +490,25 @@ export default function App() {
   };
   // Transient success toast (bottom-right, auto-dismiss). Used for things
   // like "spot sent" where a blocking error banner would be overkill.
+  // Toasts are QUEUED so two firing at once don't clobber each other: each shows
+  // for 3s, then the next takes over (no gap). `toast` is the one on screen now.
   const [toast, setToast] = useState('');
-  const showToast = useCallback((msg: string) => {
-    setToast(msg);
-    window.setTimeout(() => setToast((t) => (t === msg ? '' : t)), 3500);
+  const toastQueue = useRef<string[]>([]);
+  const toastTimer = useRef<number | undefined>(undefined);
+  const advanceToast = useCallback(() => {
+    const next = toastQueue.current.shift();
+    if (next === undefined) { toastTimer.current = undefined; setToast(''); return; }
+    setToast(next);
+    toastTimer.current = window.setTimeout(advanceToast, 3000);
   }, []);
+  const showToast = useCallback((msg: string) => {
+    toastQueue.current.push(msg);
+    if (toastTimer.current === undefined) advanceToast(); // nothing showing → start now
+  }, [advanceToast]);
+  const dismissToast = useCallback(() => {
+    if (toastTimer.current !== undefined) { window.clearTimeout(toastTimer.current); toastTimer.current = undefined; }
+    advanceToast(); // skip to the next queued toast (or clear if none)
+  }, [advanceToast]);
   // Error banners auto-dismiss after a few seconds (longer than toasts since
   // they may be multi-line). The X button still closes them immediately.
   useEffect(() => {
@@ -2878,7 +2892,7 @@ export default function App() {
                   <div className="flex items-center gap-1.5 rounded-md border border-emerald-300 bg-emerald-50 text-emerald-800 px-2.5 py-1 text-xs shadow min-w-0 animate-in fade-in">
                     <Satellite className="size-3.5 shrink-0" />
                     <span className="truncate" title={toast}>{toast}</span>
-                    <button className="shrink-0 text-emerald-600 hover:text-emerald-800" onClick={() => setToast('')}><X className="size-3" /></button>
+                    <button className="shrink-0 text-emerald-600 hover:text-emerald-800" onClick={dismissToast}><X className="size-3" /></button>
                   </div>
                 )}
               </div>