feat(astrolabe): upgrade to Vue 3 and @nextcloud/vue 9

- Merge renovate/major-vue-monorepo: Vue 2.7.16 → 3.5.26
- Merge renovate/nextcloud-vue-9.x: @nextcloud/vue 8.29.2 → 9.3.1
- Update component imports to new @nextcloud/vue v9 paths
- Replace .sync modifiers with v-model:prop (Vue 3 syntax)
- Replace beforeDestroy with beforeUnmount lifecycle hook
- Remove Vue.() usage (automatic reactivity in Vue 3)
- Update main.js to use createApp() instead of Vue.extend()
- Add @vitejs/plugin-vue and configure Vite for Vue 3
- All builds passing, ready for admin UX improvements

third_party/astrolabe/src/components/PDFViewer.vue

@@ -18,7 +18,7 @@
 import * as pdfjsLib from 'pdfjs-dist'
 import { generateUrl } from '@nextcloud/router'
 import { translate as t } from '@nextcloud/l10n'
-import NcLoadingIcon from '@nextcloud/vue/dist/Components/NcLoadingIcon.js'
+import NcLoadingIcon from '@nextcloud/vue/components/NcLoadingIcon'
 import AlertCircle from 'vue-material-design-icons/AlertCircle.vue'
 
 export default {