Accept post creation time in message contract

packages/api-contracts/tests/contracts.test.ts

@@ -96,6 +96,7 @@ describe('dashboard endpoint contracts', () => {
       modelId: 'openai/gpt-5.2',
       selectionReason: 'exploit',
       sourceType: 'image',
+      postCreatedAt: 1_699_999_900_000,
     }]).success).toBe(true);
     expect(SuccessfulExamplesResponseSchema.safeParse([{
       id: 1,