fix: add @semantic-release/npm plugin to update package.json version

[Copilot]

Semantic-release was not updating package.json with new version numbers during releases.

Changes

• Added @semantic-release/npm plugin to .releaserc.json plugins array
• Configured with npmPublish: false since package is private
• Positioned before @semantic-release/git to ensure version updates before commit

[
  "@semantic-release/npm",
  {
    "npmPublish": false
  }
]

The npm plugin's prepare step updates package.json version, which the git plugin then commits alongside CHANGELOG.md and pnpm-lock.yaml.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>semantic release issue</issue_title>
<issue_description>semantic release not updating package.json with new version number</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes semantic release issue #41

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