docs(minimax): refresh current model metadata

[octo-patch]

Reason: Refresh MiniMax model metadata and regional endpoint guidance to match the current text model configuration.

Changes

• add typed metadata for MiniMax-M3 and MiniMax-M2.7, including context windows, token pricing, input modalities, and thinking modes
• update the generated configuration guidance and README with current regional Anthropic base URLs and model capabilities
• cover both current model metadata entries in the provider test suite

Checks

• bun test tests/minimax-provider.test.ts
• bun run typecheck
• bun run build
• bun test
• prettier --check README.md src/config.ts src/services/ai/providers/minimax.ts tests/minimax-provider.test.ts