Add MiniMax-M3 default config

[octo-patch]

Reason: Add MiniMax-M3 as the default OpenAI-compatible multimodal model and document both MiniMax regional endpoints.

Changed:

• Updated config.yaml to point the OpenAI-compatible path at MiniMax global chat/completions.
• Switched the default multimodal model to MiniMax-M3.
• Clarified the request interval comment for MiniMax.

Checks:

• python3 YAML load and config assertion against config.yaml.
• Secret scan on the diff with the provided regex.