Add MiniMax M3 to model catalog

[octo-patch]

Summary

• Add MiniMax-M3 to the built-in MiniMax model catalog with 1M context and 0.6/2.4 pricing.
• Add minimax-m3 alias and make the provider default alias resolve to MiniMax-M3.
• Update catalog tests to cover the new model and default alias.

Test plan

• cargo test -p openfang-runtime model_catalog::tests::test_chinese_model_aliases (not run: cargo is not installed in the worker environment)

🤖 Generated with Claude Code

[octo-patch]

This change has been reopened cleanly as #1267 from the latest main branch, with corrected model metadata, tiered pricing, setup defaults, endpoint documentation, and tests. Closing this PR in favor of #1267.