…provider configs

- Add SiliconFlow as a new model provider with OpenAI/Anthropic format support
- Implement Gemini model listing API in Rust backend (v1beta/models endpoint)
- Update model lists: Anthropic (claude-opus-4-6, claude-sonnet-4-6),
  MiniMax (M2.5, M2.1), Qwen (3.5-Plus, 3.5-Flash), Volcengine (seed-2-0),
  Gemini (3.1-pro-preview, 3.1-flash-lite-preview)
- Fix API URLs: DeepSeek (/v1), Zhipu coding plan (/v4), Gemini base URL
- Generalize provider descriptions to remove version-specific wording
- Improve Select component styling and AIModelConfig UI refinements

Made-with: Cursor

bobleer deleted the feature/update-model-providers-and-gemini-support branch