Add publishSigned step back to release workflow

- First step: publishSigned to stage signed artifacts
- Second step: sonaRelease to release staged artifacts to Central
- Both steps needed for proper release flow

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: xerial

.github/workflows/release.yml

@@ -26,9 +26,14 @@ jobs:
         env:
           PGP_SECRET: ${{ secrets.PGP_SECRET }}
         run: echo $PGP_SECRET | base64 --decode | gpg --import --batch --yes
-      - name: Release to Sonatype
+      - name: Publish signed artifacts
         env:
           PGP_PASSPHRASE: ${{ secrets.PGP_PASSPHRASE }}
           SONATYPE_USERNAME: '${{ secrets.SONATYPE_USERNAME }}'
           SONATYPE_PASSWORD: '${{ secrets.SONATYPE_PASSWORD }}'
+        run: ./sbt publishSigned
+      - name: Release to Sonatype Central
+        env:
+          SONATYPE_USERNAME: '${{ secrets.SONATYPE_USERNAME }}'
+          SONATYPE_PASSWORD: '${{ secrets.SONATYPE_PASSWORD }}'
         run: ./sbt sonaRelease