Service Readiness now reflects real staffing status

The Service Readiness indicator no longer shows a service as fully ready when nobody has actually been scheduled to serve.

What changed

Previously, a service with no volunteer positions set up yet could still show as 100% ready if it had a plan attached. Service Readiness now factors in real staffing, so the indicator only shows a service as ready once people are actually scheduled to serve, not just when a plan exists.