[Suneha Bose (bosesuneha)]

Summary

• Update the built-in Helm fallback from v3.18.4 to v4.3.1, the current stable release.
• Update the README examples and clarify that latest is not limited to Helm 3.
• Check the fallback version and warning in the existing lookup-failure regression test.
• Preserve the retry and fallback opt-out behavior merged in fix: retry latest version lookup and add latest-fallback opt-out #303.

Validation

• All 58 tests, typecheck, build, and formatting pass under Node 24.
• Full and production npm audits report zero known vulnerabilities in JavaScript dependencies.
• Native macOS ARM64 fallback installation and cache restoration passed after three simulated lookup failures, with the published archive checksum and installed version verified.

Scope

No CHANGELOG, package-version, dependency, or workflow changes. Merging this PR does not trigger a release.

The upstream Helm binary advisory findings, including GO-2026-6809, remain a separate pre-publication follow-up.