ci: use MiniMax-M3 for PR reviews

[SaladDay]

Summary

• switch AI PR review from MiniMax-M2.7-highspeed to MiniMax-M3
• use the MiniMax CN Anthropic-compatible endpoint for the configured 操作 API key

Validation

• verified MiniMax-M3 authentication with a minimal request against the CN endpoint
• git diff --check

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