ci: deploy to Clojars on tag push

[hlship]

Summary

• Adds a Release workflow that deploys to Clojars when a numeric version tag is pushed
• Derives the library version from the git tag (or :version) instead of version.txt

Test plan

• Ensure repo secrets CLOJARS_USERNAME and CLOJARS_PASSWORD (deploy token) are set
• Merge, then push a test tag matching an unpublished version (or dry-run locally: clojure -T:build jar :version '"0.0.0-test"')
• Confirm the Release workflow runs and publishes to Clojars