Fix insecure device pairing token generation

[kolega-dev-test]

Summary

This PR fixes a security vulnerability in the device pairing token generation process. The current implementation uses a non-cryptographically secure UUID, which reduces entropy and makes the tokens susceptible to brute force attacks. This change addresses the root cause by using a cryptographically secure random token generated with crypto.randomBytes().

Changes

• Use crypto.randomBytes(32) to generate a 256-bit random token
• Encode the token as base64url (URL-safe, no padding)
• Implement token rotation and rate limiting for pairing attempts

Testing

The changes can be tested by attempting to brute force the device pairing tokens before and after the fix. The new tokens should be sufficiently secure and resistant to brute force attacks.