CodeRabbit Generated Unit Tests: Add Jest/Vitest tests for IndexedDB storage and build_library

[coderabbitai]

Unit test generation was requested by @NellowTCS.

• Migrate to Vite, add PWA/offline support, and fix table-of-contents bug (v2.1.0) #2 (comment)

The following files were modified:

• tests/build_indexedDB.test.js
• tests/build_library.test.js
• tests/helpers/indexeddb-mock.spec.js

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[NellowTCS]

i'll add needed testing framework (jest is fine) to package.json