Add Techulus host response header

[arjunkomath]

Summary

• add X-Techulus-Host to responses from generated Traefik HTTP routes
• use the control-plane server name as the header value
• preserve the existing X-Forwarded-Server request header
• verify both headers survive Traefik configuration serialization

Verification

• go test ./internal/traefik
• go build ./...
• git diff --check

Basecamp task