feat(cli): support per-command rate limiting

[huyuanfeng2018]

Summary

• add explicit per-command rate limit config via ~/.opencli/rate-limits.yaml
• block configured adapter and external CLI commands before execution with RATE_LIMITED errors
• persist sliding-window attempt state in ~/.opencli/rate-limit-state.json
• cover rate-limit parsing, adapter dispatch, and external CLI passthrough behavior in tests

Validation

• npx vitest run --project unit src/rate-limit.test.ts src/commanderAdapter.test.ts src/external.test.ts
• npm run typecheck
• npm test
• npm run build