Address Copilot review feedback on the prepare script

[vivek-perforce]

Summary

Follow-up to #5, addressing the two Copilot review comments left on that PR:

• Moves babel from devDependencies to dependencies, so the prepare script (which invokes the babel CLI via build-npm) still works when a consumer installs with dev deps omitted (npm ci --omit=dev, NODE_ENV=production). babel-core comes along transitively since it's already a dependency of the babel package itself.
• Removes the now-redundant npm run build-npm && from the release script, since prepare already runs it automatically during npm publish.

Test plan

• Simulated the failure scenario: copied the working tree to a scratch dir and ran npm install --omit=dev — prepare successfully ran babel and produced lib/*.js (this would have failed with "babel: command not found" before this fix).
• Confirmed package.json remains valid JSON.
• Did not run npm publish (not needed to verify the release script fix — confirmed via npm's documented prepare-runs-during-publish lifecycle instead).

[Copilot]

Pull request overview

This PR adjusts the npm packaging/release workflow so the prepare lifecycle can successfully build lib/ even when consumers install with dev dependencies omitted (e.g., npm ci --omit=dev), and removes redundant work from the release script.

Changes:

• Move babel from devDependencies to dependencies so npm run prepare (via build-npm) can find the babel CLI without dev deps.
• Simplify release by removing the explicit npm run build-npm &&, relying on npm’s prepare lifecycle during npm publish instead.

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