Update Ai Model Logic

[Ferdinand737]

We need to dynamically choose the AI model to optimize for cost and output quality.

When a user selects GPT-3.5 or GPT-4 that should mean they have selected that family of model, not just one specific model.

We should adjust what model we use based on the input length. We should choose the shortest context window model from models that will get the job done.

We should always use a "dumb" model for generating image search queries.