return extra field in weapon responses

was being saved but not returned, so frontend always saw it as undefined

app/blueprints/api/v1/weapon_blueprint.rb

@@ -13,7 +13,7 @@ module Api
       # Primary information
       fields :granblue_id, :element, :proficiency,
              :max_level, :max_skill_level, :max_awakening_level, :limit, :rarity,
-             :ax, :ax_type, :gacha, :promotions, :forge_order
+             :ax, :ax_type, :gacha, :promotions, :forge_order, :extra
 
       # Series - returns full object with flags if weapon_series is present, fallback to legacy integer
       field :series do |w|