Stub the custom category read in the export route tests

The full backup now reads the account's own medication categories, and
three route tests that drive the payload builder against a mocked client
had no delegate for it.

src/app/api/export/encrypted/__tests__/route.test.ts

@@ -12,6 +12,9 @@ vi.mock("@/lib/db", () => ({
   prisma: {
     measurement: { findMany: vi.fn().mockResolvedValue([]) },
     medication: { findMany: vi.fn().mockResolvedValue([]) },
+    // v1.40 — the custom medication categories the backup carries.
+    medicationCategoryLabel: { findMany: vi.fn().mockResolvedValue([]) },
+    medicationCategoryAssignment: { findMany: vi.fn().mockResolvedValue([]) },
     medicationIntakeEvent: { findMany: vi.fn().mockResolvedValue([]) },
     moodEntry: { findMany: vi.fn().mockResolvedValue([]) },
     moodTag: { findMany: vi.fn().mockResolvedValue([]) },