frontend: refactor of the new build viewer

extracting the logic into composables

frontend/composables/useItemMap.ts

@@ -0,0 +1,30 @@
+/**
+ * Composable for fetching and managing item data from CDragon API
+ * Returns a reactive Map of item ID to item data
+ */
+export const useItemMap = () => {
+  const { data: items } = useFetch<Array<Item>>('/api/cdragon/items', {
+    lazy: true,
+    server: false
+  })
+
+  const itemMap = ref<Map<number, Item>>(new Map())
+
+  watch(
+    items,
+    (newItems) => {
+      if (Array.isArray(newItems)) {
+        const map = new Map<number, Item>()
+        for (const item of newItems) {
+          if (item?.id) {
+            map.set(item.id, item)
+          }
+        }
+        itemMap.value = map
+      }
+    },
+    { immediate: true }
+  )
+
+  return { itemMap }
+}