fix: signup existing user check

[A-lexisL]

Note: current method use user_model.Object.get_or_create() to create a user, which will not call set_unusable_password, so has_usable_password will return true, leading to 409 in normal setup workflow.

[Copilot]

Pull request overview

This pull request attempts to fix an issue with the existing user check during signup. The problem stems from using get_or_create() to create users, which doesn't call set_unusable_password(), causing has_usable_password() to incorrectly return True for newly created users and triggering a false 409 error.

Changes:

• Replaces user.has_usable_password() check with user.password check in the signup endpoint

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[Copilot]

The check if user.password: is insufficient and potentially incorrect. This will treat users with unusable passwords (marked with special prefixes like "!") as if they have valid passwords, which could prevent legitimate signups.

The underlying issue is that user_model.objects.get_or_create() in create_user_session() doesn't call set_unusable_password(), leaving the password field as an empty string. A more robust solution would be to:

1. Modify create_user_session() to explicitly set an unusable password when creating new users, OR
2. Check both if the password exists AND if it's usable with a condition like: if user.password and user.has_usable_password():

The current change could block users who have unusable password markers from completing signup.

Suggested change

	if user.password:
	if user.password and user.has_usable_password():