feat: Enhance Adventure and Collection Management

- Added support for multiple collections in AdventureSerializer, allowing adventures to be linked to multiple collections.
- Implemented validation to ensure collections belong to the current user during adventure creation and updates.
- Introduced a signal to update adventure publicity based on the public status of linked collections.
- Updated file permission checks to consider multiple collections when determining access rights.
- Modified AdventureImageViewSet and AttachmentViewSet to check access against collections instead of a single collection.
- Enhanced AdventureViewSet to support filtering and sorting adventures based on collections.
- Updated frontend components to manage collections more effectively, including linking and unlinking adventures from collections.
- Adjusted API endpoints and data structures to accommodate the new collections feature.
- Improved user experience with appropriate notifications for collection actions.

backend/server/adventures/signals.py

@@ -0,0 +1,23 @@
+from django.db.models.signals import m2m_changed
+from django.dispatch import receiver
+from adventures.models import Adventure
+
+@receiver(m2m_changed, sender=Adventure.collections.through)
+def update_adventure_publicity(sender, instance, action, **kwargs):
+    """
+    Signal handler to update adventure publicity when collections are added/removed
+    """
+    # Only process when collections are added or removed
+    if action in ('post_add', 'post_remove', 'post_clear'):
+        collections = instance.collections.all()
+        
+        if collections.exists():
+            # If any collection is public, make the adventure public
+            has_public_collection = collections.filter(is_public=True).exists()
+            
+            if has_public_collection and not instance.is_public:
+                instance.is_public = True
+                instance.save(update_fields=['is_public'])
+            elif not has_public_collection and instance.is_public:
+                instance.is_public = False
+                instance.save(update_fields=['is_public'])