fix: export named DB utilities in petsExtendedFields test mock

pets.ts imports pets, appointments, and, eq, exists, or directly from
"../db". The vi.mock factory only returned getDb, causing vitest to throw
"No 'pets' export is defined" and 7 tests to get 400 instead of 201/200.
Fix adds the missing named exports to the mock return object.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/api/src/__tests__/petsExtendedFields.test.ts

@@ -161,6 +161,12 @@ vi.mock("../db", () => {
       update: () => makeUpdateChainable(),
       delete: () => makeDeleteChainable(),
     }),
+    pets,
+    appointments,
+    and,
+    eq,
+    exists,
+    or,
   };
 });