fix collection creation

backend/src/main/java/com/storycove/service/CollectionService.java

@@ -190,10 +190,13 @@ public class CollectionService {
      */
     public Map<String, Object> addStoriesToCollection(UUID collectionId, List<UUID> storyIds, Integer startPosition) {
         Collection collection = findByIdBasic(collectionId);
-        
+
+        // Deduplicate story IDs before validation (UI may send duplicates due to event handling)
+        List<UUID> uniqueStoryIds = storyIds.stream().distinct().collect(java.util.stream.Collectors.toList());
+
         // Validate stories exist
-        List<Story> stories = storyRepository.findAllById(storyIds);
-        if (stories.size() != storyIds.size()) {
+        List<Story> stories = storyRepository.findAllById(uniqueStoryIds);
+        if (stories.size() != uniqueStoryIds.size()) {
             throw new ResourceNotFoundException("One or more stories not found");
         }
         
@@ -203,7 +206,7 @@ public class CollectionService {
         // Get starting position
         int position = startPosition != null ? startPosition : collectionStoryRepository.getNextPosition(collectionId);
         
-        for (UUID storyId : storyIds) {
+        for (UUID storyId : uniqueStoryIds) {
             // Check if story is already in collection
             if (collectionStoryRepository.existsByCollectionIdAndStoryId(collectionId, storyId)) {
                 skipped++;

frontend/src/components/collections/CollectionForm.tsx

@@ -359,6 +359,7 @@ export default function CollectionForm({
                           type="checkbox"
                           checked={isSelected}
                           onChange={() => toggleStorySelection(story)}
+                          onClick={(e) => e.stopPropagation()}
                           className="rounded border-gray-300 text-blue-600 focus:ring-blue-500"
                         />
                         <div className="flex-1 min-w-0">