Fix critical collection persistence bug where initial items disappeared after first enhancement by implementing database-first pattern with template-based reconstruction

internal/content/mock.go

@@ -174,3 +174,11 @@ func (m *MockClient) GetCollectionItems(siteID, collectionID string) ([]engine.C
 func (m *MockClient) CreateCollectionTemplate(siteID, collectionID, name, htmlTemplate string, isDefault bool) (*engine.CollectionTemplateItem, error) {
 	return nil, fmt.Errorf("collection operations not implemented in MockClient")
 }
+
+func (m *MockClient) GetCollectionTemplates(siteID, collectionID string) ([]engine.CollectionTemplateItem, error) {
+	return nil, fmt.Errorf("collection operations not implemented in MockClient")
+}
+
+func (m *MockClient) CreateCollectionItem(siteID, collectionID, itemID string, templateID int, htmlContent string, position int, lastEditedBy string) (*engine.CollectionItemWithTemplate, error) {
+	return nil, fmt.Errorf("collection operations not implemented in MockClient")
+}