Add a service to scope groups via JWT authentication (External API).

This endpoint provides the same functionality as POST /api/internal/add-to-groups but uses modern JWT Bearer token authentication.

Authentication: JWT Bearer token (via nginx X-User header) Authorization: Requires valid JWT token from auth system

Request body (form data):

• server_name (required): Service name
• group_names (required): Comma-separated list of group names

Response: Returns confirmation of group assignment.

Example:

curl -X POST https://registry.example.com/api/servers/groups/add \
  -H "Authorization: Bearer $JWT_TOKEN" \
  -F "server_name=myservice" \
  -F "group_names=admin,developers"