CodeRabbit Generated Unit Tests: Add comprehensive Jest unit tests for backend modules

[coderabbitai]

Unit test generation was requested by @rx6ru.

• Concize v3 #1 (comment)

The following files were modified:

• backend/tests/clean.test.js
• backend/tests/embeddingService.test.js
• backend/tests/geminiService.test.js
• backend/tests/groqService.test.js
• backend/tests/queryVectordb.test.js
• backend/tests/tempAuthCheck.test.js

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