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/main.js

@@ -1,8 +1,11 @@
-import Vue from 'vue'
+import { createApp } from 'vue'
 import { translate as t, translatePlural as n } from '@nextcloud/l10n'
 import App from './App.vue'
 
-Vue.mixin({ methods: { t, n } })
+const app = createApp(App)
 
-const View = Vue.extend(App)
-new View().$mount('#astrolabe')
+// Add translation methods globally
+app.config.globalProperties.t = t
+app.config.globalProperties.n = n
+
+app.mount('#astrolabe')