feat: add MiniMax provider support

[octo-patch]

Reason: Add MiniMax provider routing with the current model catalog and regional endpoints.

Changes:

• Registers MiniMax in the canonical provider registry with current model metadata, pricing, modality, thinking, and regional endpoint details.
• Adds MiniMax models to the selector through registry metadata.
• Wires MiniMax chat routing through the OpenAI-compatible endpoint with a configurable base URL.

Checks:

• bun test src/providers.test.ts src/utils/model.test.ts src/model/llm.test.ts
• npm run typecheck
• bun test

[octo-patch]

I updated MiniMax routing to support both OpenAI-compatible and Anthropic-compatible global and CN endpoints, and pushed commit 070ef61. I ran the focused MiniMax tests, bun run typecheck, and the full bun test suite (320 tests); the new GitHub CI run is also passing.