Add Atomic Chat as a local model provider — PR feedback welcome

[yanalialiuk]

We use Atomic Chat as a local OpenAI-compatible server (http://127.0.0.1:1337/v1/). I opened a PR to add it to Continue as provider atomic-chat:

#12438

Summary: new provider class + Add Model entry (fetches models from /v1/models, no API key), CLI/docs, tests. Small UI fix so switching providers doesn’t apply a stale model list.

Would appreciate a look when someone has time — happy to change anything to match project conventions.