Enhance month view overlay with preview, auto-scroll, and 1s delay

- Fix backend type comparison in AvailabilityService (int vs string)
- Add durationMinutes to month overlay drop to fix end_time calculation
- Add live preview of dragged appointment in overlay with lane splitting
- Implement horizontal auto-scroll when dragging to overlay edges
- Add 1-second delay before overlay appears for easier date navigation
- Remove redundant drop zone highlight (preview shows position)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

smoothschedule/schedule/serializers.py

@@ -82,7 +82,7 @@ class ResourceSerializer(serializers.ModelSerializer):
         fields = [
             'id', 'name', 'type', 'description', 'max_concurrent_events',
             'buffer_duration', 'is_active', 'capacity_description',
-            'created_at', 'updated_at',
+            'saved_lane_count', 'created_at', 'updated_at',
         ]
         read_only_fields = ['created_at', 'updated_at']
     
@@ -196,16 +196,28 @@ class EventSerializer(serializers.ModelSerializer):
     def validate(self, attrs):
         """
         Validate event timing and resource availability.
-        
+
         Checks:
         1. end_time > start_time
         2. start_time not in past (for new events)
         3. Resource availability using AvailabilityService
         """
+        # For partial updates, get existing values from instance if not provided
         start_time = attrs.get('start_time')
         end_time = attrs.get('end_time')
         resource_ids = attrs.get('resource_ids', [])
-        
+
+        # If this is a partial update, fill in missing values from existing instance
+        if self.instance:
+            if start_time is None:
+                start_time = self.instance.start_time
+            if end_time is None:
+                end_time = self.instance.end_time
+
+        # Skip validation if we still don't have both times (shouldn't happen for valid requests)
+        if start_time is None or end_time is None:
+            return attrs
+
         # Validation 1: End must be after start
         if end_time <= start_time:
             raise serializers.ValidationError({

smoothschedule/schedule/services.py

@@ -48,7 +48,8 @@ class AvailabilityService:
             event = participant.event
             
             # Skip if this is the event being updated
-            if exclude_event_id and event.id == exclude_event_id:
+            # CRITICAL: Convert exclude_event_id to int for comparison (frontend may send string)
+            if exclude_event_id and event.id == int(exclude_event_id):
                 continue
             
             # CRITICAL: Skip cancelled events (prevents ghost bookings)