Add MiniMax provider support (#656 by @dannote)

- Add minimax to KnownProvider and Api types
- Add MINIMAX_API_KEY to getEnvApiKey()
- Generate MiniMax-M2 and MiniMax-M2.1 models
- Add context overflow detection pattern
- Add tests to all required test files
- Update README and CHANGELOG with attribution

Also fixes:
- Bedrock duplicate toolResult ID when content has multiple blocks
- Sandbox extension unused parameter lint warning

packages/coding-agent/src/cli/args.ts

@@ -243,6 +243,8 @@ ${chalk.bold("Environment Variables:")}
   XAI_API_KEY             - xAI Grok API key
   OPENROUTER_API_KEY      - OpenRouter API key
   ZAI_API_KEY             - ZAI API key
+  MISTRAL_API_KEY         - Mistral API key
+  MINIMAX_API_KEY         - MiniMax API key
   AWS_PROFILE             - AWS profile for Amazon Bedrock
   AWS_ACCESS_KEY_ID       - AWS access key for Amazon Bedrock
   AWS_SECRET_ACCESS_KEY   - AWS secret key for Amazon Bedrock