feat(ui): use modal dialogs for entity creation and editing

Introduce reusable Modal component for forms
Update router to preserve scroll position when toggling modals
Refactor admin and entity views to render editors as overlays

frontend/src/views/ItemsList.vue

@@ -1,6 +1,7 @@
 <script setup lang="ts">
 import { computed, onMounted, ref, watch } from 'vue';
 import { useI18n } from 'vue-i18n';
+import { useRoute } from 'vue-router';
 import EditMeta from '../components/EditMeta.vue';
 import EntityChips from '../components/EntityChips.vue';
 import EntityCard from '../components/EntityCard.vue';
@@ -10,8 +11,10 @@ import Skeleton from '../components/Skeleton.vue';
 import Tabs, { type TabOption } from '../components/Tabs.vue';
 import TagsSelect from '../components/TagsSelect.vue';
 import { api, type Item, type Options } from '../services/api';
+import ItemEdit from './ItemEdit.vue';
 
 const options = ref<Options | null>(null);
+const route = useRoute();
 const { t } = useI18n();
 const items = ref<Item[]>([]);
 const loading = ref(true);
@@ -35,6 +38,7 @@ const itemQuery = computed(() => ({
   usageId: usageId.value,
   tagIds: tagIds.value.join(',')
 }));
+const showEditor = computed(() => route.name === 'item-new');
 
 async function loadItems() {
   loading.value = true;
@@ -134,5 +138,7 @@ watch(itemQuery, loadItems);
         <EntityChips :items="item.tags" />
       </EntityCard>
     </div>
+
+    <ItemEdit v-if="showEditor" />
   </section>
 </template>