feat: 401 auth-failure handling — suspend after N, typed errors (#16)

[AndresL230]

Summary

• Adds RecostError / RecostAuthError / RecostFatalAuthError to the public API; mirrors Python's pre-declared hierarchy.
• Suspends the cloud transport after maxConsecutiveAuthFailures (default 5) consecutive 401s. Recovery is restart-only.
• One-time stderr warning on first 401 + second stderr line at fatal-suspend, both regardless of debug flag.
• Existing onError(err: Error) signature is unchanged — hosts narrow via instanceof.

Closes #16.

Test plan

• npm run test — 228/228 green (219 baseline + 9 new cases)
• npm run lint — clean
• npm run build — clean dual ESM + CJS + DTS
• Manually verify a fresh consumer can import RecostAuthError from @recost-dev/node in both ESM and CJS

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: af542290-1919-4f9d-8751-18280470badd

📥 Commits

Reviewing files that changed from the base of the PR and between 32dbbe5 and b58a512.

📒 Files selected for processing (7)

• README.md
• docs/superpowers/plans/2026-05-13-401-auth-failure-handling.md
• docs/superpowers/specs/2026-05-13-401-auth-failure-handling-design.md
• src/core/transport.ts
• src/core/types.ts
• src/index.ts
• tests/transport.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/401-auth-failure-handling

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