fix release workflow: skip tag push if tag exists, bump Node to lts/*

Prevented exit-128 crash when a fix commit pushes to master at the same
version — the workflow now checks for an existing remote tag before
attempting to push one, so the release step can still create the GitHub
release even if the tag is already there.

Also updated both workflows from node-version 20.x to lts/* ahead of the
GitHub-enforced Node 24 migration deadline (2026-06-02).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Use Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: "20.x"
+          node-version: "lts/*"
           cache: "npm"
 
       - name: Install dependencies

.github/workflows/release.yml

@@ -29,12 +29,17 @@ jobs:
           else
             echo "exists=false" >> $GITHUB_OUTPUT
           fi
+          if git ls-remote --tags origin "${{ steps.version.outputs.version }}" | grep -q .; then
+            echo "tag_exists=true" >> $GITHUB_OUTPUT
+          else
+            echo "tag_exists=false" >> $GITHUB_OUTPUT
+          fi
 
       - name: Use Node.js
         if: steps.check.outputs.exists == 'false'
         uses: actions/setup-node@v4
         with:
-          node-version: "20.x"
+          node-version: "lts/*"
           cache: "npm"
 
       - name: Install dependencies
@@ -57,8 +62,10 @@ jobs:
           version="${{ steps.version.outputs.version }}"
           git config user.name "github-actions[bot]"
           git config user.email "github-actions[bot]@users.noreply.github.com"
-          git tag -a "$version" -m "$version"
-          git push origin "$version"
+          if [ "${{ steps.check.outputs.tag_exists }}" != "true" ]; then
+            git tag -a "$version" -m "$version"
+            git push origin "$version"
+          fi
           gh release create "$version" \
             --title="$version" \
             --generate-notes \