v0.2.0

feat: AI cleanup with Groq, OpenRouter, and NVIDIA NIM providers

- post-transcription LLM pass: prompts enhanced, messages grammar-fixed
- optional translate-to-English toggle (tone-matched)
- free-tier providers with encrypted key storage and Test key button
- live model list fetched from the provider
- new 'Polishing with AI' overlay state; cleanup errors surfaced
- bump version to 0.2.0