Refactor AI Providers, features and models

[brainless]

As an engineer I want a better way to manage the Rust code to organise AI providers, their features and models. Some AI providers do not have embedding API for example. We want to store the features and pricing in the local SQLite database and sync from our online storage with a new API.

The Rust code would handle features per provider and accordingly set (user may select) the model if needed. In this case it may also make sense to store pricing information in code since they are directly tied to feature and model as handled by Rust.