fix(documents): repair inline add-item modal on invoice/estimate create

Render a single shared ItemModal (was one per row, so stacked dialogs closed each other), validate the modal's own local form (vuelidate did not track the shared store object in the persistent modal), surface save errors, and carry the typed item name into the new-item form.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

resources/scripts/features/shared/document-form/DocumentItemsTable.vue

@@ -1,5 +1,9 @@
 <template>
   <div class="rounded-xl border border-line-light shadow bg-surface">
+    <!-- Single shared item-create modal for the whole table (one instance, not one
+         per row — stacked HeadlessUI dialogs would otherwise close each other). -->
+    <ItemModal />
+
     <!-- Tax Included Toggle -->
     <div
       v-if="taxIncludedSetting === 'YES'"
@@ -109,6 +113,7 @@
 import { computed } from 'vue'
 import draggable from 'vuedraggable'
 import DocumentItemRow from './DocumentItemRow.vue'
+import ItemModal from '@/scripts/features/company/items/components/ItemModal.vue'
 import type { Currency } from '../../../types/domain/currency'
 import type { DocumentFormData } from './use-document-calculations'