docs: document port exposure model for catalog services (osaas-catalog-manager#313) Add Developer-Guide:-Port-Exposure-Model.md explaining the single-HTTP-port model, the four unsupported service categories (extra TCP ports, UDP, dynamic relay port ranges, self-managed TLS on 443), the port budget rationale from ADR-0032, options for services that do not fit, and the three historical operator-managed exceptions. Co-Authored-By: Claude <noreply@anthropic.com>