Guard release job against non-tag workflow_dispatch runs

Add `if: startsWith(github.ref, 'refs/tags/')` to the release job
so workflow_dispatch triggers can test build without failing on
the gh-release action which requires a tag ref.

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

Author: stephenleo

.github/workflows/release.yml

@@ -64,6 +64,7 @@ jobs:
 
   release:
     name: Publish GitHub Release
+    if: startsWith(github.ref, 'refs/tags/')
     needs: build
     runs-on: ubuntu-latest
     permissions: