Adjust Zammad AI provider after product/plan clarification

[ralf401]

• Remove remark that it is only limited to specific customers
• Maybe add what plan is required and how to upgrade

12.12.2025:

• Zammad AI also available for self-hosted customers
• First manual process, they have to get in touch with sales via web form
• SaaS customers need a V2 plan and then they can buy AI calls in the subscription module

[ralf401]

This is already solved with #1010 / #1025 => Closing