fix(ci): skip npm publish if version already exists on npm registry

Prevents E403 failures when a release event fires more than once for the
same version (e.g. re-running a failed workflow or duplicate tag event).

The publish step now checks whether the version is already on npm and
exits cleanly with a warning instead of failing the workflow.

.github/workflows/npm-publish.yml

@@ -39,6 +39,13 @@ jobs:
         run: node scripts/prepublish.mjs
 
       - name: Publish to npm
-        run: npm publish --access public
+        run: |
+          VERSION=$(node -p "require('./package.json').version")
+          # Check if this version is already published — skip instead of failing with E403
+          if npm view "omniroute@${VERSION}" version --silent 2>/dev/null | grep -q "^${VERSION}$"; then
+            echo "️⚠️ Version ${VERSION} is already published on npm — skipping."
+            exit 0
+          fi
+          npm publish --access public
         env:
           NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}