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/package-lock.json

@@ -12,6 +12,7 @@
         "qrcode.react": "^4.2.0",
         "react": "^19.2.0",
         "react-dom": "^19.2.0",
+        "react-hot-toast": "^2.6.0",
         "react-router-dom": "^7.9.5",
         "socket.io-client": "^4.8.1"
       },
@@ -4168,7 +4169,6 @@
       "version": "3.1.3",
       "resolved": "https://registry.npmjs.org/csstype/-/csstype-3.1.3.tgz",
       "integrity": "sha512-M1uQkMl8rQK/szD0LNhtqxIPLpimGm8sOBwU7lLnCpSbTyY3yeU1Vc7l4KT5zT4s/yOxHH5O7tIuuLOCnLADRw==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/data-urls": {
@@ -5402,6 +5402,15 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
+    "node_modules/goober": {
+      "version": "2.1.18",
+      "resolved": "https://registry.npmjs.org/goober/-/goober-2.1.18.tgz",
+      "integrity": "sha512-2vFqsaDVIT9Gz7N6kAL++pLpp41l3PfDuusHcjnGLfR6+huZkl6ziX+zgVC3ZxpqWhzH6pyDdGrCeDhMIvwaxw==",
+      "license": "MIT",
+      "peerDependencies": {
+        "csstype": "^3.0.10"
+      }
+    },
     "node_modules/gopd": {
       "version": "1.2.0",
       "resolved": "https://registry.npmjs.org/gopd/-/gopd-1.2.0.tgz",
@@ -7274,6 +7283,23 @@
         "react": "^19.2.0"
       }
     },
+    "node_modules/react-hot-toast": {
+      "version": "2.6.0",
+      "resolved": "https://registry.npmjs.org/react-hot-toast/-/react-hot-toast-2.6.0.tgz",
+      "integrity": "sha512-bH+2EBMZ4sdyou/DPrfgIouFpcRLCJ+HoCA32UoAYHn6T3Ur5yfcDCeSr5mwldl6pFOsiocmrXMuoCJ1vV8bWg==",
+      "license": "MIT",
+      "dependencies": {
+        "csstype": "^3.1.3",
+        "goober": "^2.1.16"
+      },
+      "engines": {
+        "node": ">=10"
+      },
+      "peerDependencies": {
+        "react": ">=16",
+        "react-dom": ">=16"
+      }
+    },
     "node_modules/react-is": {
       "version": "17.0.2",
       "resolved": "https://registry.npmjs.org/react-is/-/react-is-17.0.2.tgz",