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

cmd/serve.go

@@ -238,6 +238,9 @@ func runServe(cmd *cobra.Command, args []string) {
 			collectionRouter.Post("/{id}/items", contentHandler.CreateCollectionItem)
 			collectionRouter.Put("/{id}/items/{item_id}", contentHandler.UpdateCollectionItem)
 			collectionRouter.Delete("/{id}/items/{item_id}", contentHandler.DeleteCollectionItem)
+
+			// Bulk operations
+			collectionRouter.Put("/{id}/reorder", contentHandler.ReorderCollection)
 		})
 	})
 
@@ -286,6 +289,7 @@ func runServe(cmd *cobra.Command, args []string) {
 	fmt.Printf("     POST   /api/collections/{id}/items\n")
 	fmt.Printf("     PUT    /api/collections/{id}/items/{item_id}\n")
 	fmt.Printf("     DELETE /api/collections/{id}/items/{item_id}\n")
+	fmt.Printf("     PUT    /api/collections/{id}/reorder\n")
 	fmt.Printf("🌐 Static sites:\n")
 	for siteID, _ := range siteManager.GetAllSites() {
 		fmt.Printf("   %s: http://localhost%s/sites/%s/\n", siteID, addr, siteID)