Migrate npm publishing to trusted publishers (#496)

Switch from manual NPM_TOKEN authentication to OpenID Connect (OIDC)
trusted publishing. This provides better security by:
- Eliminating the need to manage long-lived NPM tokens as secrets
- Using short-lived OIDC tokens generated by GitHub Actions
- Adding provenance attestations to published packages

Changes:
- Add id-token: write and contents: read permissions
- Use --provenance flag for npm publish
- Remove NODE_AUTH_TOKEN secret usage

Requires configuration on npmjs.com to add GitHub Actions as a
trusted publisher before this workflow will work.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <[email protected]>

Author: ryanio

.github/workflows/npm-publish.yml

@@ -10,6 +10,9 @@ on:
 jobs:
   publish-npm:
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      id-token: write
     steps:
       - uses: actions/checkout@v5
       - uses: actions/setup-node@v6
@@ -19,6 +22,4 @@ jobs:
       - run: npm ci
       - run: npm run build
       - run: npm test
-      - run: npm publish
-        env:
-          NODE_AUTH_TOKEN: ${{secrets.npm_token}}
+      - run: npm publish --provenance --access public