Auto-logout users when page is closed

- Create LogoutOnUnload component that triggers logout on page close
- Uses beforeunload/unload events with navigator.sendBeacon() for reliability
- Create /api/logout endpoint that clears both admin and customer sessions
- Add LogoutOnUnload to root layout so it runs on all pages
- Works for both admin and customer users

Behavior:
- When user closes browser tab/window, logout happens automatically
- Session cookies are cleared via API endpoint
- Improves security by preventing session hijacking from closed windows

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/app/api/logout/route.ts

@@ -0,0 +1,14 @@
+import { cookies } from 'next/headers';
+import { NextResponse } from 'next/server';
+
+export async function POST() {
+  const cookieStore = await cookies();
+
+  // Clear admin session
+  cookieStore.delete('adminSession');
+
+  // Clear customer session
+  cookieStore.delete('session');
+
+  return NextResponse.json({ success: true });
+}