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/DropdownMenu.vue

@@ -0,0 +1,15 @@
+<script setup lang="ts">
+import type { DropdownMenuRootEmits, DropdownMenuRootProps } from "reka-ui"
+import { DropdownMenuRoot, useForwardPropsEmits } from "reka-ui"
+
+const props = defineProps<DropdownMenuRootProps>()
+const emits = defineEmits<DropdownMenuRootEmits>()
+
+const forwarded = useForwardPropsEmits(props, emits)
+</script>
+
+<template>
+  <DropdownMenuRoot v-bind="forwarded">
+    <slot />
+  </DropdownMenuRoot>
+</template>