Added category contract

Necessary to validate the Contracts API response.

Milestone: minor

lib/trmnl/api/container.rb

@@ -20,6 +20,7 @@ module TRMNL
       end
 
       namespace :contracts do
+        register :category, Contracts::Category
         register :current_screen, Contracts::CurrentScreen
         register :display, Contracts::Display
         register :firmware, Contracts::Firmware

lib/trmnl/api/contracts/category.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require "dry/schema"
+
+module TRMNL
+  module API
+    module Contracts
+      # Validates API response.
+      Category = Dry::Schema.JSON { required(:data).array(:string) }
+    end
+  end
+end