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/Avatar.vue

@@ -0,0 +1,22 @@
+<script setup lang="ts">
+import type { HTMLAttributes } from "vue"
+import type { AvatarVariants } from "."
+import { AvatarRoot } from "reka-ui"
+import { cn } from '~/lib/utils'
+import { avatarVariant } from "."
+
+const props = withDefaults(defineProps<{
+  class?: HTMLAttributes["class"]
+  size?: AvatarVariants["size"]
+  shape?: AvatarVariants["shape"]
+}>(), {
+  size: "sm",
+  shape: "circle",
+})
+</script>
+
+<template>
+  <AvatarRoot :class="cn(avatarVariant({ size, shape }), props.class)">
+    <slot />
+  </AvatarRoot>
+</template>