feat: track received image outcomes

packages/api-contracts/src/stats.ts

@@ -5,6 +5,8 @@ const PerformanceFields = {
   totalSent: z.number(),
   totalResponses: z.number(),
   responseRate: z.number(),
+  totalImages: z.number(),
+  imageRate: z.number(),
 };
 
 export const StatsResponseSchema = z.strictObject({