fix: ensure dist folder is built before npm publish

[zanussbaum]

Problem

The latest npm release (v1.0.12) is missing the dist folder, making the package unusable since the main entry point is dist/index.js. This happened because:

1. The dist folder is in .gitignore (correctly)
2. The release workflow publishes to npm without building the project first
3. The package.json specifies "files": ["dist"] but the folder doesn't exist during publish

Solution

This PR adds two layers of protection:

1. Build step in release workflow: Added npm run build step before publishing in .github/workflows/release-please.yml
2. prepublishOnly script: Added "prepublishOnly": "npm run build" to package.json as a safety net

Testing

Tested with npm publish --dry-run which now correctly:

• Runs the prepublishOnly script
• Builds the dist folder
• Includes all 66 files (82.2 kB unpacked) in the package

Impact

• Fixes the broken v1.0.12 npm package
• Prevents future releases from missing the dist folder
• No breaking changes to existing functionality