fix(ctrl): Add fallback for null defaultOrganization during OIDC login

[Vaishnav88sk]

Fixes the NullPointerException during OIDC login when a user's defaultOrganization is unset.
The AuthenticationController now checks if the default organization is null. If it is, it automatically falls back to the first organization the user is a member of, allowing JWT token generation to succeed gracefully.

Related Issues:
Fixes #182

[lbroudoux]

I would have used 403 instead of 400 and I think some code can be extracted into the same utilitty method to avoid duplication.

[Vaishnav88sk]

You are completely right about the 403 Forbidden - that is much more semantically accurate since the request is valid but lacks permissions. I will also extract the organization resolution and token generation logic into a single utility method to DRY up the controller. Since I have less experience with code architecture, I sometimes make mistakes in these situations 😉.

I'll push those changes up shortly!

[Vaishnav88sk]

I've just pushed an update to address both points:

1. Changed 400 to 403 Forbidden: You're absolutely right! Since the request is perfectly valid and the user is authenticated, but they just lack the required organization membership, a 403 Forbidden is the semantically correct status code.
2. Extracted Utility Method: I pulled the duplicated organization resolution and token generation logic into a single resolveOrganizationAndGenerateToken utility method to keep the controller DRY.

Let me know if everything looks good!

[lbroudoux]

This looks all good. Thanks for the changes.