[Test]: Add unit tests for `validatePassword` in `backend/src/utils/validations.ts`

What feature do you want?

Description: validatePassword (backend/src/utils/validations.ts:14) is used by auth.service.ts to validate passwords on signup, but it currently has no test coverage. It has 5 independent branches (minimum length, requireNumber, requireLowercase, requireUppercase, requireSpecialChar) that should each be exercised.

Every sibling function in the same file (validateEmail, escapeSqlLikePattern, etc.) already has tests in backend/tests/unit/validations.test.ts — validatePassword is the one gap.

Why do you need this?

Add these unit test to make validate Suggested approach:

• Add a describe('validatePassword', ...) block to backend/tests/unit/validations.test.ts.
• Cover: passing password, too-short password, and one failing case per rule flag (requireNumber, requireLowercase, requireUppercase, requireSpecialChar), plus a case with multiple flags combined.