fix: add concurrency to release workflow to prevent race conditions (#38)

When multiple PRs merge in quick succession, parallel release jobs
race on git push and npm publish, causing failures. This serializes
release jobs so they queue instead of running concurrently.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: cablate

.github/workflows/release.yml

@@ -4,6 +4,10 @@ on:
   push:
     branches: [main]
 
+concurrency:
+  group: release
+  cancel-in-progress: false
+
 jobs:
   release:
     # Skip automated version bump commits