test(db): add unit tests for test factories (GitHub #94)

Tests cover resetFactoryCounters(), counter determinism, override
merging, and compile-time enforcement of required fields on
buildAppointment. All 16 new tests pass (92 total).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/package.json

@@ -27,11 +27,11 @@
     "@types/node": "^22.10.7",
     "@types/node-cron": "^3.0.11",
     "@types/nodemailer": "^6.4.17",
-    "@vitest/coverage-v8": "^3.0.4",
+    "@vitest/coverage-v8": "^3.2.4",
     "eslint": "^9.18.0",
     "tsx": "^4.19.2",
     "typescript": "^5.7.3",
     "typescript-eslint": "^8.20.0",
-    "vitest": "^3.0.4"
+    "vitest": "^3.2.4"
   }
 }