feat(frontend): add toast notifications for dashboard actions

- Install react-hot-toast library
- Add Toaster component to App.jsx
- Show success/error toasts for match accept/reject/cancel
- Show toasts for real-time match events
- Update tests with toast mocks

frontend/src/App.jsx

@@ -1,4 +1,5 @@
 import { BrowserRouter, Routes, Route, Navigate } from 'react-router-dom';
+import { Toaster } from 'react-hot-toast';
 import { AuthProvider, useAuth } from './contexts/AuthContext';
 import HomePage from './pages/HomePage';
 import LoginPage from './pages/LoginPage';
@@ -70,6 +71,30 @@ function App() {
         {/* PWA Install Prompt */}
         <InstallPWA />
 
+        {/* Toast Notifications */}
+        <Toaster
+          position="top-right"
+          toastOptions={{
+            duration: 4000,
+            style: {
+              background: '#333',
+              color: '#fff',
+            },
+            success: {
+              iconTheme: {
+                primary: '#22c55e',
+                secondary: '#fff',
+              },
+            },
+            error: {
+              iconTheme: {
+                primary: '#ef4444',
+                secondary: '#fff',
+              },
+            },
+          }}
+        />
+
         <Routes>
           {/* Public Routes */}
           <Route