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/dropdown-menu/DropdownMenuShortcut.vue

@@ -0,0 +1,14 @@
+<script setup lang="ts">
+import type { HTMLAttributes } from "vue"
+import { cn } from '~/lib/utils'
+
+const props = defineProps<{
+  class?: HTMLAttributes["class"]
+}>()
+</script>
+
+<template>
+  <span :class="cn('ml-auto text-xs tracking-widest opacity-60', props.class)">
+    <slot />
+  </span>
+</template>