feat: Refactor GraphQL resolvers to extract domain methods into separate files and retain only shared helpers

- Add package documentation mapping resolver files to domains (subscriber/usage/billing/mutations/esim/alerts/subscriptions)
- Remove models package import and add blank imports for context/base64 to preserve helper function dependencies
- Remove all resolver method implementations (Subscriber/SubscriberByImsi/Subscribers/SubscriberAccount/UsageEvents/UsageStats/RealTimeUsage/Invoices/Invoice

apps/api-server/internal/graphql/resolvers_mutations.go

@@ -0,0 +1,87 @@
+package graphql
+
+import (
+	"context"
+
+	"github.com/nutcas3/telecom-platform/apps/api-server/internal/models"
+	"github.com/nutcas3/telecom-platform/apps/api-server/internal/services"
+)
+
+// CreateSubscriber creates a new subscriber from GraphQL input.
+func (r *Resolver) CreateSubscriber(ctx context.Context, input CreateSubscriberInput) (*models.Subscriber, error) {
+	req := &services.CreateSubscriberRequest{
+		MSISDN:    input.MSISDN,
+		FirstName: input.FirstName,
+		LastName:  input.LastName,
+		Email:     input.Email,
+		PlanID:    uint(input.PlanID),
+	}
+	if input.OrganizationID != nil {
+		req.OrganizationID = *input.OrganizationID
+	}
+	if input.EUICCID != nil {
+		req.EUICCID = *input.EUICCID
+	}
+	return r.subscriber.CreateSubscriber(ctx, req)
+}
+
+// UpdateSubscriber updates subscriber fields.
+func (r *Resolver) UpdateSubscriber(ctx context.Context, id string, input UpdateSubscriberInput) (*models.Subscriber, error) {
+	sid, err := parseID(id)
+	if err != nil {
+		return nil, err
+	}
+	var planID *uint
+	if input.PlanID != nil {
+		p := uint(*input.PlanID)
+		planID = &p
+	}
+	return r.subscriber.UpdateSubscriber(ctx, sid, &services.UpdateSubscriberRequest{
+		FirstName: input.FirstName,
+		LastName:  input.LastName,
+		Email:     input.Email,
+		PlanID:    planID,
+	})
+}
+
+// DeleteSubscriber deletes a subscriber by GraphQL ID.
+func (r *Resolver) DeleteSubscriber(ctx context.Context, id string) (bool, error) {
+	sid, err := parseID(id)
+	if err != nil {
+		return false, err
+	}
+	return r.subscriber.DeleteSubscriber(ctx, sid)
+}
+
+// SuspendSubscriber suspends and returns the refreshed subscriber.
+func (r *Resolver) SuspendSubscriber(ctx context.Context, id string) (*models.Subscriber, error) {
+	sid, err := parseID(id)
+	if err != nil {
+		return nil, err
+	}
+	if err := r.subscriber.SuspendSubscriber(ctx, sid); err != nil {
+		return nil, err
+	}
+	return r.subscriber.GetSubscriber(ctx, sid)
+}
+
+// ActivateSubscriber activates and returns the subscriber.
+func (r *Resolver) ActivateSubscriber(ctx context.Context, id string) (*models.Subscriber, error) {
+	sid, err := parseID(id)
+	if err != nil {
+		return nil, err
+	}
+	return r.subscriber.ActivateSubscriber(ctx, sid)
+}
+
+// TerminateSubscriber terminates and returns the refreshed subscriber.
+func (r *Resolver) TerminateSubscriber(ctx context.Context, id string) (*models.Subscriber, error) {
+	sid, err := parseID(id)
+	if err != nil {
+		return nil, err
+	}
+	if err := r.subscriber.TerminateSubscriber(ctx, sid); err != nil {
+		return nil, err
+	}
+	return r.subscriber.GetSubscriber(ctx, sid)
+}