feature: local TTS option

[sammcj]

Howdy, neat project!

I found it pretty easy to swap out OpenAI with a compatible local LLM endpoint (via Ollama w/ Qwen 2.5) but it would be fantastic if there was a local TTS option to completely remove the need for OpenAI.

[artnoage]

Do you think you could try to add one (local TTS) and then we do a pull request? This way we can also include your modifications for local llm endpoints.