chore: replace shrinkwrap with package lock

[trivikr]

npm-shrinkwrap.json was added in #134 to pin the transitive dependencies of gitlint-parser-node.

Since #144 moved that package into this repository, the only remaining runtime dependency is the dependency-free gitlint-parser-base.

This PR:

• Pins gitlint-parser-base to 2.0.0.
• Replaces the published shrinkwrap with a development-only package-lock.json.
• Avoids publishing dev-dependency metadata.

This will be required to work with npm 12, which has removed support for npm-shrinkwrap.json.

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Assisted-by: codex:gpt-5.6-sol