fix: handle re-inviting users with expired invitations

[maartenbode]

Summary

• Fixes UniqueConstraintViolationException when re-inviting a user whose previous invitation has expired
• The pendingInvitations() scope filters out expired invites (expires_at > now()), so the duplicate check in MemberController::store doesn't catch them, but the DB unique constraint on (organization_uuid, email) blocks the insert
• Changed OrganizationInvitation::create() to updateOrCreate() so expired invitations get refreshed (new token, expiry, role, inviter) instead of causing a duplicate key error