重构：移除环境变量管理员初始化

backend/internal/service/merchant_test.go

@@ -336,26 +336,3 @@ func TestListMerchantAccountGroupsExcludesPlatformAdmins(t *testing.T) {
 		t.Fatalf("unexpected merchant account group: %+v", groups[0])
 	}
 }
-
-func TestEnsureAdminUsesConfiguredCredentialsOnlyForEmptyDatabase(t *testing.T) {
-	db := newServiceTestDB(t)
-	tenant := NewTenantService(db)
-	auth := NewAuthService(db, nil, tenant)
-	if err := auth.EnsureAdmin("skin_nh_admin", "secure-password"); err != nil {
-		t.Fatalf("create configured admin: %v", err)
-	}
-	var created model.User
-	if err := db.Where("username = ?", "skin_nh_admin").First(&created).Error; err != nil {
-		t.Fatalf("configured admin should exist: %v", err)
-	}
-	if err := bcrypt.CompareHashAndPassword([]byte(created.PasswordHash), []byte("secure-password")); err != nil {
-		t.Fatalf("configured password should match: %v", err)
-	}
-	if err := auth.EnsureAdmin("replacement-admin", "another-password"); err != nil {
-		t.Fatalf("existing admin should not be replaced: %v", err)
-	}
-	var count int64
-	if err := db.Model(&model.User{}).Where("role = ?", model.RoleAdmin).Count(&count).Error; err != nil || count != 1 {
-		t.Fatalf("existing admin should remain unchanged, count=%d err=%v", count, err)
-	}
-}