feat(chat_v2): add MiniMax AI as LLM provider

[octo-patch]

Summary

• Add MiniMax AI as a third model provider in the chat demo alongside Local (vLLM) and HeyWhale API
• Users can now select "MiniMax AI" from the Model Provider dropdown and use cloud-hosted MiniMax-M2.7 models without running a local model service
• Includes MiniMax-specific temperature clamping (0.01-1.0) and API key management in both backend and frontend

Changes

Backend (demo/chat_v2/backend_app/services/chat.py):

• _iter_minimax_stream(): new streaming function using OpenAI-compatible SDK with MiniMax base URL
• _normalize_minimax_temperature(): clamps temperature to MiniMax-accepted range [0.01, 1.0]
• Extended build_chat_runtime_config() with minimax provider routing, auto-defaults for API base and model
• Updated bot_stream() dispatch to route minimax provider to the new stream iterator

Frontend (demo/chat_v2/frontend/components/three-panel-interface.tsx):

• Added MiniMax AI option in Model Provider Select dropdown
• Added MiniMax API Key input with sessionStorage persistence
• Validation: blocks send if MiniMax is selected without API key
• Sends correct model name (MiniMax-M2.7) when MiniMax provider is active

Documentation (README.md, README_ZH.md):

• Listed MiniMax AI as a supported provider in features
• Added note about using MiniMax without local model service

Test plan

• 27 unit tests: temperature clamping, config building, stream mocking, provider routing (all pass)
• 3 integration tests: live MiniMax API calls for basic completion, streaming, temperature (all pass)
• Manual: select MiniMax AI in UI, enter API key, send a data analysis prompt
• Verify Local and HeyWhale providers still work unchanged

[LIUyizheSDU]

Is the API base https://api.minimaxi.com/v1? I’ve registered a MiniMax account, but my API key doesn’t work with https://api.minimaxi.io/v1.

[octo-patch]

Thanks for trying it out @LIUyizheSDU!

The correct API base URL for MiniMax is:

https://api.minimax.io/v1

Note: It's minimax.io, not minimaxi.com. The URL in the code should already be set correctly. If you're seeing issues, please double-check:

1. Your API key is valid (you can get one from the MiniMax platform)
2. The base URL in the configuration is https://api.minimax.io/v1

Let me know if you run into any other issues!