feat(frontend-auth): add NextAuth.js v5 Keycloak integration (partial - Task 10)

- Install next-auth@5.0.0-beta.30 and @auth/core@0.34.3
- Configure Keycloak OIDC provider with JWT and session callbacks
- Add module augmentation for JWT and Session types (clubs claim support)
- Export auth handlers and configuration

INCOMPLETE: Missing middleware.ts, useActiveClub() hook, API utility, and tests
Will complete in follow-up session resumption

frontend/package.json

@@ -9,10 +9,12 @@
     "lint": "eslint"
   },
   "dependencies": {
+    "@auth/core": "^0.34.3",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "lucide-react": "^0.576.0",
     "next": "16.1.6",
+    "next-auth": "^5.0.0-beta.30",
     "next-themes": "^0.4.6",
     "radix-ui": "^1.4.3",
     "react": "19.2.3",