Add first-class MiniMax provider support

[octo-patch]

Reason: Add first-class MiniMax dispatch with current models and regional compatibility endpoints.

Changes:

• Register MiniMax-M3 and MiniMax-M2.7 with context, pricing, cache, modality, and thinking metadata.
• Add credential-based direct dispatch with global and China endpoint selection for both supported compatibility protocols.
• Document the runtime settings and add focused registry, endpoint, pricing, and routing coverage.

Checks:

• pnpm exec vitest run src/lib/__tests__/minimax.test.ts src/lib/__tests__/models.test.ts src/lib/__tests__/token-pricing.test.ts src/lib/__tests__/task-dispatch.test.ts
• pnpm typecheck
• pnpm lint