Implement collection item reordering with bulk operations and persistent HTML attributes

- Add bulk reorder API endpoint (PUT /api/collections/{id}/reorder) with atomic transactions
- Replace individual position updates with efficient bulk operations in frontend
- Implement unified ID generation and proper data-item-id injection during enhancement
- Fix collection item position persistence through content edit cycles
- Add optimistic UI with rollback capability for better user experience
- Update sqlc queries to include last_edited_by fields in position updates
- Remove obsolete data-content-type attributes and unify naming conventions

internal/engine/engine.go

@@ -3,7 +3,6 @@ package engine
 import (
 	"fmt"
 	"strings"
-	"time"
 
 	"golang.org/x/net/html"
 )
@@ -103,8 +102,8 @@ func (e *ContentEngine) ProcessContent(input ContentInput) (*ContentResult, erro
 		// Generate structural ID for the collection container
 		collectionID := e.idGenerator.Generate(collectionElem.Node, input.FilePath)
 
-		// Add data-content-id attribute to the collection container
-		e.setAttribute(collectionElem.Node, "data-content-id", collectionID)
+		// Add data-collection-id attribute to the collection container
+		e.setAttribute(collectionElem.Node, "data-collection-id", collectionID)
 
 		// Process collection during enhancement or content injection
 		if input.Mode == Enhancement || input.Mode == ContentInjection {
@@ -243,7 +242,6 @@ func (e *ContentEngine) addContentAttributes(node *html.Node, contentID string)
 	e.setAttribute(node, "data-content-id", contentID)
 }
 
-
 // setAttribute sets an attribute on an HTML node
 func (e *ContentEngine) setAttribute(node *html.Node, key, value string) {
 	// Remove existing attribute if it exists
@@ -377,8 +375,6 @@ func (e *ContentEngine) extractHTMLContent(node *html.Node) string {
 	return strings.TrimSpace(content.String())
 }
 
-
-
 // extractOriginalTemplate extracts the outer HTML of the element (including the element itself)
 func (e *ContentEngine) extractOriginalTemplate(node *html.Node) string {
 	var buf strings.Builder
@@ -549,6 +545,12 @@ func (e *ContentEngine) extractAndStoreTemplatesAndItems(collectionNode *html.No
 		return fmt.Errorf("failed to store initial collection items: %w", err)
 	}
 
+	// Reconstruct items from database to ensure proper data-item-id injection
+	err = e.reconstructCollectionItems(collectionNode, collectionID, siteID)
+	if err != nil {
+		return fmt.Errorf("failed to reconstruct initial collection items: %w", err)
+	}
+
 	return nil
 }
 
@@ -619,6 +621,12 @@ func (e *ContentEngine) reconstructCollectionItems(collectionNode *html.Node, co
 			for structuralChild := structuralBody.FirstChild; structuralChild != nil; {
 				next := structuralChild.NextSibling
 				structuralBody.RemoveChild(structuralChild)
+
+				// Inject data-item-id attribute for collection item identification
+				if structuralChild.Type == html.ElementNode {
+					e.setAttribute(structuralChild, "data-item-id", item.ItemID)
+				}
+
 				collectionNode.AppendChild(structuralChild)
 				structuralChild = next
 			}
@@ -730,15 +738,18 @@ func (e *ContentEngine) CreateCollectionItemFromTemplate(
 	templateHTML string,
 	lastEditedBy string,
 ) (*CollectionItemWithTemplate, error) {
-	// Generate unique item ID
-	itemID := fmt.Sprintf("%s-item-%d", collectionID, time.Now().Unix())
-
 	// Create virtual element from template (like enhancement path)
 	virtualElement, err := e.createVirtualElementFromTemplate(templateHTML)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create virtual element: %w", err)
 	}
 
+	// Generate unique item ID using unified generator with collection context
+	itemID := e.idGenerator.Generate(virtualElement, "collection-item")
+	if err != nil {
+		return nil, fmt.Errorf("failed to create virtual element: %w", err)
+	}
+
 	// Process .insertr elements and create content entries (unified approach)
 	contentEntries, err := e.processChildElementsAsContent(virtualElement, siteID, itemID)
 	if err != nil {
@@ -808,8 +819,8 @@ func (e *ContentEngine) storeChildrenAsCollectionItems(collectionNode *html.Node
 
 	// Store each child using unified .insertr approach (content table + structural template)
 	for i, childElement := range childElements {
-		// Generate item ID (like content ID generation)
-		itemID := fmt.Sprintf("%s-initial-%d", collectionID, i+1)
+		// Generate item ID using unified generator with collection context
+		itemID := e.idGenerator.Generate(childElement, "collection-item")
 
 		// Process .insertr elements within this child (unified approach)
 		contentEntries, err := e.processChildElementsAsContent(childElement, siteID, itemID)