[FEATURE]: Add unit tests for indexedDbHelpers

Scenario

Given the indexedDbHelpers.ts utility provides CRUD functions for images in IndexedDB,
When developers write unit tests for each helper function,
Then data persistence, retrieval, and error handling should be verified with automated tests.

Acceptance Criteria

• Test suite tests/indexedDbHelpers.test.ts created.
• Covers all CRUD helper functions.
  • Create
  • Read
  • Update
  • Delete
• Tests pass locally and in CI.
• Documentation/comments in test file for future contributors.

Additional Context

Reference file: utils/indexedDbHelpers.ts

Jest testing framework documentation https://jestjs.io/docs/getting-started

IndexedDB documentation: https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API

IndexedDB is used in:

• https://github.com/oss-slu/image-recognition-integration-system/blob/main/app/utils/indexedDbHelpers.ts
• https://github.com/oss-slu/image-recognition-integration-system/blob/main/app/components/cameraButton.tsx
• https://github.com/oss-slu/image-recognition-integration-system/blob/main/app/imageGallery/page.tsx