feat: tag items depending on region and gold state when bought

frontend/types/api.ts

@@ -1,4 +1,9 @@
 declare global {
+  /**
+   * Item tags derived from purchase patterns
+   */
+  type ItemTag = 'ahead' | 'behind' | 'region_euw' | 'region_eun' | 'region_na' | 'region_kr'
+
   /**
    * Represents an item in the build tree
    */
@@ -6,6 +11,7 @@ declare global {
     count: number
     data: number
     children: ItemTree[]
+    tags: ItemTag[]
   }
 
   /**