feat: add MiniMax provider support

[octo-patch]

Summary

Adds MiniMax as a provider option in Shannon's router mode, enabling users to use MiniMax models as an alternative to Anthropic Claude.

Changes

• apps/cli/infra/router-config.json: Add minimax provider entry with OpenAI-compatible API endpoint (https://api.minimax.io/v1/chat/completions) and models MiniMax-M2.7 and MiniMax-M2.7-highspeed
• apps/cli/infra/compose.yml: Pass MINIMAX_API_KEY environment variable to the router container
• .env.example: Document MiniMax configuration option and available models

Usage

To use MiniMax with Shannon router mode:

# In your .env file:
MINIMAX_API_KEY=your-minimax-api-key
ROUTER_DEFAULT=minimax,MiniMax-M2.7

# Start with router mode:
./shannon start ... ROUTER=true

MiniMax Models

Model	Description
MiniMax-M2.7	Peak Performance. Ultimate Value. Master the Complex
MiniMax-M2.7-highspeed	Same performance, faster and more agile

API reference:

• Chat (OpenAI Compatible): https://platform.minimax.io/docs/api-reference/text-openai-api