Implement Password Grant Flow for Authentication and Enhance User Experience

- Introduced Password Grant Flow for user authentication, allowing direct login with email and password.
- Updated `useAuth` composable to manage login and logout processes, including Single Sign-Out from Cidaas.
- Enhanced user interface with a new `UserMenu` component displaying user information and logout functionality.
- Updated homepage to show personalized greetings for logged-in users and a login prompt for guests.
- Added logout confirmation page with a countdown redirect to the homepage.
- Documented the implementation details and future enhancements for OAuth2 flows in CLAUDE.md and other relevant documentation.
- Added test credentials and guidelines for automated testing in the new TESTING.md file.

package.json

@@ -19,6 +19,7 @@
   "dependencies": {
     "@nuxtjs/i18n": "^10.1.2",
     "@vee-validate/zod": "^4.15.1",
+    "@vueuse/core": "^14.0.0",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "drizzle-orm": "^0.44.7",