ci: publish via npm trusted publishing (OIDC), drop NPM_TOKEN (#282)

Authenticate the release workflow through GitHub OIDC instead of a long-lived
npm token: no secret to leak or rotate, provenance attached automatically.
Upgrade npm on the runner since OIDC publishing needs npm >= 11.5.1 (Node 22
ships npm 10).

.github/workflows/publish.yml

@@ -17,7 +17,8 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: '22'
-          registry-url: 'https://registry.npmjs.org'
-      - run: npm publish --provenance --access public
-        env:
-          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}
+      # Trusted publishing (OIDC) needs npm >= 11.5.1; Node 22 ships npm 10.
+      - run: npm install -g npm@latest
+      # No token: id-token: write above lets npm authenticate via OIDC, and
+      # provenance is attached automatically. access set in publishConfig.
+      - run: npm publish