chore: remove unused reusable workflows

Keep only workflows actively used by audiospacelive and ai-dev-env:
- docker-build-push.yml (audiospacelive)
- gitleaks-scan.yml (ai-dev-env)
- trivy-scan.yml (ai-dev-env)
- sbom-generate.yml (ai-dev-env)
- helm-publish.yml (ai-dev-env)

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

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

Author: samuelho-dev