fix: detect stale deployment and prompt user to refresh (#388)

When a new version is deployed while users have the page open,
Next.js Server Actions fail with hash mismatches. This adds a
global listener that catches the specific error and shows a
persistent toast prompting the user to refresh.

Closes the issue reported by @thisismissem where editing broke
after a deployment.

src/app/layout.tsx

···
 import { getLocale, getMessages } from 'next-intl/server';
 import { ThemeProvider } from '@/components/theme-provider';
 import { KonamiRickroll } from '@/components/konami-rickroll';
+import { StaleDeploymentDetector } from '@/components/stale-deployment-detector';
 import { Toaster } from 'sonner';
 import './globals.css';
 
···
           >
             {children}
             <KonamiRickroll />
+            <StaleDeploymentDetector />
             <Toaster position="bottom-left" closeButton />
           </ThemeProvider>
         </NextIntlClientProvider>

src/components/stale-deployment-detector.tsx

···
+'use client';
+
+import { useEffect, useRef } from 'react';
+import { toast } from 'sonner';
+
+const SERVER_ACTION_ERROR = 'Failed to find Server Action';
+const TOAST_ID = 'stale-deployment';
+
+export function StaleDeploymentDetector() {
+  const shownRef = useRef(false);
+
+  useEffect(() => {
+    function handleRejection(event: PromiseRejectionEvent) {
+      const message = event.reason?.message ?? String(event.reason ?? '');
+      if (!message.includes(SERVER_ACTION_ERROR)) return;
+      if (shownRef.current) return;
+      shownRef.current = true;
+
+      toast.error('Sifa has been updated since you opened this page.', {
+        id: TOAST_ID,
+        duration: Infinity,
+        description: 'Please refresh to continue editing.',
+        action: {
+          label: 'Refresh now',
+          onClick: () => window.location.reload(),
+        },
+      });
+    }
+
+    window.addEventListener('unhandledrejection', handleRejection);
+    return () => window.removeEventListener('unhandledrejection', handleRejection);
+  }, []);
+
+  return null;
+}