Add test coverage for existing-unverified-user OTP branch in signup

[coderabbitai]

Problem

The test suite added in PR #141 (apps/public-api/src/__tests__/userAuth.email.test.js) does not cover the existing-unverified-user resend branch inside controller.signup (the code path that fires when a user who already registered but never verified their email tries to sign up again).

This path also generates an OTP and, without a test, could silently regress back to Math.random() without failing any tests.

Desired Change

Add a test case to the OTP generation uses CSPRNG suite that:

1. Simulates a signup attempt with an already-registered but unverified email.
2. Asserts that crypto.randomInt is called with (100000, 1000000) on that code path.

Context

Identified during review of PR #141 (Fix/weak OTP generation). The main PRNG fix is complete (#105); this is a test-coverage follow-up.

PR reference: #141
Raised by: @yash-pouranik

[itsmessc]

assign this to me i will finish it off

[yash-pouranik]

hm yes
proceed
@itsmessc