Make Caddy host port configurable

[shrkz1]

Summary

• add ERAMBA_HOST_PORT=8443 to the project .env
• use it for the published side of the Caddy public_proxy port mapping while keeping the internal target fixed at 443
• document its relationship with PUBLIC_ADDRESS and clarify that Apache ports.conf and the virtual host do not need changes
• add a Compose contract test proving an override resolves to 9443:443

Why

Customers can select the Docker host port in .env without editing the tracked Compose file. PUBLIC_ADDRESS remains an independent external-origin setting because a reverse proxy or load balancer may expose a different public port. Caddy, Eramba, and MCP retain their fixed internal ports.

Validation

• npx --no-install bats@1.12.0 tests/mcp-simple-install.bats (5/5 passed)
• Community Compose configuration validated with the default port
• Enterprise overlay validated with ERAMBA_HOST_PORT=9443
• override resolved to 9443:443
• git diff --check origin/1.x...HEAD