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.

app/components/ui/avatar/AvatarImage.vue

@@ -0,0 +1,12 @@
+<script setup lang="ts">
+import type { AvatarImageProps } from "reka-ui"
+import { AvatarImage } from "reka-ui"
+
+const props = defineProps<AvatarImageProps>()
+</script>
+
+<template>
+  <AvatarImage v-bind="props" class="h-full w-full object-cover">
+    <slot />
+  </AvatarImage>
+</template>