feat(models): add Together AI provider and update model catalog for v0.8.55
- Add Together AI as a first-class provider (ProviderKind::Together)
- Config block [providers.together], env TOGETHER_API_KEY/TOGETHER_BASE_URL/TOGETHER_MODEL
- Default models: deepseek-ai/DeepSeek-V4-Pro, deepseek-ai/DeepSeek-V4-Flash
- Base URL: https://api.together.xyz/v1
- TUI ApiProvider::Together with picker, auth, and capability support
- CLI auth list/status support
- Add model catalog entries:
- Qwen 3.7 Max (qwen/qwen3.7-max on OpenRouter)
- MiniMax 2.7 (minimax/minimax-2.7 on OpenRouter)
- NVIDIA Nemotron 3 Ultra (nvidia/nemotron-3-ultra on OpenRouter)
- Update docs/PROVIDERS.md, docs/CONFIGURATION.md, config.example.toml
- Update check-provider-registry.py compatible surfaces
- Fix provider picker tests for new provider count
Closes #2906, #2907, #2910, #2912, #2913
Hunter Bown
c13bc24805