fix(examagent): restore Moodle API compatibility and fix multi-environment template handling

[Copilot]

The exam agent InstanceAdapter broke Moodle compatibility when multi-environment template support was introduced: the JSON field names changed (contentUrls → split into customizationUrls), and InstanceSpecFromAdapter hardcoded "default" as the environment key in ContentUrls, which fails whenever the template's environment isn't named "default".

Changes

• New CustomizationUrls struct — matches the expected Moodle-facing API:

  type CustomizationUrls struct {
      ContentOrigin      string `json:"contentOrigin,omitempty"`
      ContentDestination string `json:"contentDestination,omitempty"`
      StatusCheck        string `json:"statusCheck,omitempty"`
  }

• InstanceAdapter — replaces ContentUrls clv1alpha2.InstanceContentUrls (json: contentUrls) with CustomizationUrls CustomizationUrls (json: customizationUrls), restoring the expected wire format.

• InstanceSpecFromAdapter — now accepts context.Context and client.Client, fetches the referenced Template at call time to resolve the actual first environment name as the ContentUrls map key, populates StatusCheckURL from CustomizationUrls.StatusCheck, and returns an error if the template contains more than one environment (unsupported by the exam agent).

• HandlePut — calls InstanceSpecFromAdapter before ctrl.CreateOrUpdate and handles the new error return.

• AdapterFromInstance — maps inst.Spec.ContentUrls (first entry) and inst.Spec.StatusCheckURL back into the new CustomizationUrls fields on the adapter.