fix(astrolabe): address review feedback for Vue 3 bindings

- Change limit initialization from string '20' to number 20 in App.vue
- Update AdminSettings.vue NcTextField to use v-model instead of legacy
  :value/@update:value bindings
- Update AdminSettings.vue NcSelect components to use :model-value with
  computed getters and @update:model-value for proper object-to-id
  conversion (same pattern as App.vue)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

third_party/astrolabe/src/App.vue

@@ -443,7 +443,7 @@ export default {
 			algorithm: 'hybrid',
 			showAdvanced: false,
 			selectedDocTypes: [],
-			limit: '20',
+			limit: 20,
 			scoreThreshold: 0,
 			loading: false,
 			error: null,