docs: add MiniMax M3 models and regional endpoints

[octo-patch]

Reason: add target provider/model to existing provider registry

Summary

• add MiniMax-M3 and MiniMax-M2.7 aliases with context, modality, thinking, and pricing metadata
• document global and mainland China base URLs for both supported API protocols
• align the existing MiniMax provider example with the model table

Checks

• git diff --check
• target matrix validation for both models and every regional/protocol endpoint combination
• configured secret-pattern scan