Added .env.example file with all AI service configuration placeholders.
Users should copy this to .env and fill in their actual API keys.
The .env file is already in .gitignore and will not be committed.
This allows users to configure Mistral, Vosk, and Coqui services without
committing sensitive API keys to git.
Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>
