Use snapshot mode for manual workflow dispatch (#4)

## Summary
- Fix release workflow failing when triggered manually via
`workflow_dispatch`
- GoReleaser requires a git tag for `release` — manual triggers now use
`build --snapshot --clean` instead
- Tag-triggered runs continue using `release --clean` as before

## Test plan
- [ ] Trigger workflow manually from GitHub Actions UI — should succeed
with snapshot build
- [ ] Push a `v*` tag — should create a full release as before

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

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

Author: juhgiyo

.github/workflows/release.yml

@@ -26,6 +26,6 @@ jobs:
         uses: goreleaser/goreleaser-action@v7
         with:
           version: "~> v2"
-          args: release --clean
+          args: ${{ github.event_name == 'workflow_dispatch' && 'build --snapshot --clean' || 'release --clean' }}
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}