refactor(forms): Migrate Forms.vue to Vue 3 Composition API

- Converted component to use Vue 3's Composition API with setup()
- Removed duplicate function declarations and fixed syntax issues
- Updated lifecycle hooks to use onMounted/onUnmounted
- Fixed reactivity using ref and computed
- Cleaned up event handling and component structure
- Ensured compatibility with Vue 3 and Nextcloud ecosystem

Author: nfebe