Fix npm publish workflow for trusted publishing (#143)

Cloeses o1-labs/o1js-site#3.
Sibling of PR #142.

## Summary

- Remove `registry-url` from `actions/setup-node`: it generates an
`.npmrc` that conflicts with npm's OIDC trusted publishing
authentication
- Add `--provenance` to `npm publish`: signs the package with a build
attestation linking it to this repo and workflow
- Add `workflow_dispatch` trigger: allows manual publishes from the
GitHub Actions UI

- NOTE: 
- This PR does everything as PR [#142
](#142.). However #142
didn't add `--provenance`. Without it, the `id-token: write` permission
is set up but never actually used. The OIDC token gets requested but
`npm publish` doesn't attach it as a signed attestation to the package.
So it's a fix on top of what PR #142 had.


## Publishing process

### Pre-release steps

1. Bump the version in `package.json` (e.g. `npm version patch` /
`minor` / `major`)
2. Commit the version bump
3. Tag the commit: `git tag v<version>` (e.g. `git tag v0.1.0`)
4. Push both: `git push origin main --tags`

The workflow triggers automatically on the `v*` tag push. It will:
1. Install dependencies (`npm ci`)
2. Build the package (`npm run build`)
3. Run tests (`npm test`)
4. Publish to npm with provenance attestation

Alternatively, you can trigger the workflow manually from the [Actions
tab](../../actions/workflows/publish-npm.yml) using "Run workflow" on
any branch.

### Prerequisites

- npm trusted publishing must be configured for this package on
npmjs.com, linking it to this GitHub repo (already done by Leon)
- The version in `package.json` must not already be published on npm

## Test plan
- [ ] Trigger workflow manually via `workflow_dispatch` to verify it
authenticates and publishes correctly
- [ ] Verify the published package on `npmjs.com` shows provenance
information

Author: Shigoto-dev19

.github/workflows/publish-npm.yml

@@ -1,6 +1,7 @@
 name: Publish Package
 
 on:
+  workflow_dispatch:
   push:
     tags:
       - 'v*'
@@ -18,12 +19,11 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: '20'
-          registry-url: 'https://registry.npmjs.org'
 
       # Ensure npm 11.5.1 or later is installed
       - name: Update npm
         run: npm install -g npm@latest
       - run: npm ci
       - run: npm run build --if-present
       - run: npm test
-      - run: npm publish
+      - run: npm publish --provenance