Clean up preview repo workflows

Remove development workflows that should only run on fork:
- ci-dte.yml (comprehensive testing - fork only)
- ci-preview.yml (legacy)
- deploy-all.yml, deploy-dev.yml (development deployments)
- nx-optimized-ci.yml (Nx Cloud CI - fork only)
- nx-smart-deploy.yml (development tooling)

Keeps only preview-ci.yml for lightweight deployment validation.

This aligns with dual CI architecture where:
- Fork: Comprehensive testing with Nx Cloud
- Preview: Lightweight validation for client deployment

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

Co-Authored-By: Claude <[email protected]>

Author: jonphipps