refactor(registry): remove obsolete ZIP version guard

[TheRealBecks]

isZipVersionEntry has no production callers, and its meaning changed when HTML-index releases were introduced.

Remove the helper and its barrel export. Update existing tests to use isExplicitVersionEntry and direct source-type assertions, preserving ZIP and HTML-index coverage.

Addresses the obsolete-helper follow-up in #151.

Validation: lint, production builds, and all 103 registry tests passed.

[changeset-bot]

⚠️ No Changeset found

Latest commit: a4d86e9

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[human0-bot]

Approved — removes the unused guard and preserves ZIP and HTML-index coverage.

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