feat(ci): migrate to npm OIDC trusted publishing (Fission-AI#390)

Replace classic npm token authentication with OIDC trusted publishing:

- Add `id-token: write` permission for OIDC token generation
- Upgrade to Node 24 (includes npm 11.5.1+ required for OIDC)
- Remove NPM_TOKEN/NODE_AUTH_TOKEN env vars (OIDC replaces them)

This eliminates the need for rotating npm access tokens and provides
cryptographically verified publisher identity with automatic provenance
attestation.

Requires configuring trusted publisher on npmjs.com:
- Organization: Fission-AI
- Repository: OpenSpec
- Workflow: release-prepare.yml

Author: TabishB

.github/workflows/release-prepare.yml

@@ -7,6 +7,7 @@ on:
 permissions:
   contents: write
   pull-requests: write
+  id-token: write # Required for npm OIDC trusted publishing
 
 concurrency:
   group: release-${{ github.ref }}
@@ -27,11 +28,9 @@ jobs:
 
       - uses: actions/setup-node@v4
         with:
-          node-version: '20'
+          node-version: '24' # Node 24 includes npm 11.5.1+ required for OIDC
           cache: 'pnpm'
           registry-url: 'https://registry.npmjs.org'
-          scope: '@fission-ai'
-          always-auth: true
 
       - run: pnpm install --frozen-lockfile
 
@@ -46,5 +45,4 @@ jobs:
           publish: pnpm run release:ci
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
-          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}
+          # npm authentication handled via OIDC trusted publishing (no token needed)