Implement emergency fallback model switch via environment variable in AI Gateway

Description

To quickly improve our resilience against AI service outages, we need to implement basic fallback capabilities. This issue outlines the immediate steps we'll take.

Tasks

• Create an MR to add a simple environment variable in the AI Gateway to specify a fallback model
• Identify 1-2 key features that require fallback prompts
• Develop and implement fallback prompts for the identified features
• Test the fallback mechanism with the new environment variable and prompts

Acceptance Criteria:

• Fallback model can be specified via an environment variable in AI Gateway
• At least one key feature has a working fallback prompt implemented
• Team members are aware of how to activate the fallback in case of an emergency