test: update toJson mock factories for doctor-report-prefs + healthkit

The v1.4.34.3 code-quality batch added a `toJson<T>()` helper in
`src/lib/db.ts` to consolidate the seven Prisma JSON-cast sites.
Two existing route tests mock the entire `@/lib/db` module via
`vi.mock` — those mock factories now need to expose the new export
so the route's import resolves to a real function under test.

The mock implementation is the identity cast (`<T>(v: T) => v`),
which matches what production does and keeps the test's JSON-payload
assertions stable.

src/app/api/auth/me/doctor-report-prefs/__tests__/route.test.ts

@@ -7,6 +7,7 @@ vi.mock("@/lib/db", () => ({
       update: vi.fn(),
     },
   },
+  toJson: <T,>(v: T) => v,
 }));
 
 vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));

src/app/api/integrations/healthkit/__tests__/route.test.ts

@@ -5,6 +5,7 @@ vi.mock("@/lib/db", () => ({
   prisma: {
     user: { findUnique: vi.fn(), update: vi.fn() },
   },
+  toJson: <T,>(v: T) => v,
 }));
 
 vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));