Add cloud models

Add cloud models for enhancing transcribed text (bring your own API key)

For example, when writing a text (which can be set to a different hotkey), it will transcribe the audio and use AI to enhance it a little.

Start by reviewing the legacy Swift macOS app's existing transcription flow and configurable hotkey behavior. Clarify which cloud models are supported, how a user supplies an API key, and how enhancement follows transcription; done means the feature works without exposing the key and produces the intended enhanced text.

Written by the indexing model from the issue text.