feat(ECR-014): MembershipPlan 套餐配置并 Closed

membership_plans 表、admin 套餐页、Grant/CreateOrder 读表；
Loop continuous 自动 Approve/Closed。Next：ECR-015 RedemptionCode。

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/internal/service/admin/membership_plans.go

@@ -0,0 +1,86 @@
+package admin
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+
+	"github.com/google/uuid"
+
+	"github.com/yuxingu/digital-psychology/apps/api/internal/repository"
+)
+
+var (
+	ErrPlanNotFound = errString("plan not found")
+	ErrInvalidPlanU = errString("invalid plan update")
+)
+
+// ListMembershipPlans returns catalog.
+func (s *Service) ListMembershipPlans(ctx context.Context) ([]repository.MembershipPlanRow, error) {
+	items, err := s.Repo.ListMembershipPlans(ctx)
+	if err != nil {
+		return nil, err
+	}
+	if items == nil {
+		items = []repository.MembershipPlanRow{}
+	}
+	return items, nil
+}
+
+// GetMembershipPlan returns one plan.
+func (s *Service) GetMembershipPlan(ctx context.Context, code string) (*repository.MembershipPlanRow, error) {
+	p, err := s.Repo.GetMembershipPlan(ctx, code)
+	if err != nil {
+		return nil, err
+	}
+	if p == nil {
+		return nil, ErrPlanNotFound
+	}
+	return p, nil
+}
+
+// UpdateMembershipPlan updates mutable fields.
+func (s *Service) UpdateMembershipPlan(
+	ctx context.Context, adminID uuid.UUID, code, title string, days, amount int, active bool,
+) (*repository.MembershipPlanRow, error) {
+	code = strings.TrimSpace(code)
+	title = strings.TrimSpace(title)
+	if title == "" || days <= 0 || amount < 0 {
+		return nil, ErrInvalidPlanU
+	}
+	if _, err := s.GetMembershipPlan(ctx, code); err != nil {
+		return nil, err
+	}
+	meta, _ := json.Marshal(map[string]any{
+		"title": title, "duration_days": days, "amount_cents": amount, "active": active,
+	})
+	if err := s.Repo.UpdateMembershipPlanWithAudit(ctx, adminID, code, title, days, amount, active, meta); err != nil {
+		return nil, err
+	}
+	return s.GetMembershipPlan(ctx, code)
+}
+
+// PlanDurationDays resolves grant length from catalog with hardcoded fallback.
+func (s *Service) PlanDurationDays(ctx context.Context, plan string) (int, error) {
+	p, err := s.Repo.GetMembershipPlan(ctx, plan)
+	if err != nil {
+		return 0, err
+	}
+	if p != nil && p.Active && p.DurationDays > 0 {
+		return p.DurationDays, nil
+	}
+	return planDaysFallback(plan)
+}
+
+func planDaysFallback(plan string) (int, error) {
+	switch plan {
+	case "month":
+		return 31, nil
+	case "quarter":
+		return 92, nil
+	case "year":
+		return 366, nil
+	default:
+		return 0, ErrInvalidPlan
+	}
+}