Fix collection manager JavaScript errors after attribute naming changes

- Update collection manager to use data-collection-id instead of data-content-id
- Add safety checks to prevent undefined Map access in addItemControls
- Add validation in editor to only initialize collections with valid collection IDs
- Resolves TypeError and missing attribute errors in frontend collection management

lib/src/ui/collection-manager.js

@@ -18,9 +18,9 @@ export class CollectionManager {
         this.auth = auth;
         
         // Extract collection ID from container
-        this.collectionId = this.container.getAttribute('data-content-id');
+        this.collectionId = this.container.getAttribute('data-collection-id');
         if (!this.collectionId) {
-            console.error('❌ Collection container missing data-content-id attribute');
+            console.error('❌ Collection container missing data-collection-id attribute');
             return;
         }
         
@@ -331,7 +331,7 @@ export class CollectionManager {
      * Add management controls to an item (remove, reorder)
      */
     addItemControls(itemElement, index) {
-        if (this.itemControls.has(itemElement)) return; // Already has controls
+        if (!this.itemControls || this.itemControls.has(itemElement)) return; // Already has controls or not initialized
         
         const controls = document.createElement('div');
         controls.className = 'insertr-item-controls';