fix(cli): handle unsupported CLI versions

[nkavian]

Summary

• send default CLI headers on unauthenticated form requests so every InFlow API call can participate in server-side version checks
• parse server problem envelopes into stable InflowApiError codes/messages
• surface VERSION_UNSUPPORTED as an actionable upgrade error with the install instructions link

Verification

• pnpm format:check
• pnpm typecheck
• pnpm lint
• pnpm test (rerun with loopback permission after sandbox EPERM on 127.0.0.1)
• pnpm typedoc
• pnpm build (rerun with permission to publish generated static skill assets into inflow-server)
• pnpm --filter @inflowpayai/inflow exec pnpm publish --dry-run --no-git-checks
• git diff --check

[codecov]

Codecov Report

❌ Patch coverage is 80.35714% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
packages/core/src/resources/auth.ts	11.11%	8 Missing ⚠️
packages/core/src/resources/api-error.ts	91.89%	2 Missing and 1 partial ⚠️

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