Fix: Preserve stream order in ChannelSerializer PATCH/PUT responses

The ChannelSerializer.to_representation() method was not respecting the
ChannelStream.order field when serializing PATCH/PUT responses. This
caused streams to be returned in an arbitrary order rather than the
order specified in the request.

The update() method correctly saves the stream order to the database
using the ChannelStream.order field, and GET requests (with
include_streams=True) correctly return ordered streams via
get_streams(). However, standard PATCH/PUT responses were using
PrimaryKeyRelatedField which doesn't respect the ordering.

This fix ensures that all representations (GET, PATCH, PUT) return
streams ordered by the channelstream__order field.

Impact:
- PATCH/PUT responses now correctly reflect the stream order saved
- Clients can trust the response data without needing a follow-up GET
- No breaking changes - only fixes inconsistent behavior

Tested with:
- PATCH request with ordered stream IDs
- Verified response matches request order
- Verified GET request confirms order persisted to database

apps/channels/serializers.py

@@ -348,8 +348,17 @@ class ChannelSerializer(serializers.ModelSerializer):
 
         if include_streams:
             self.fields["streams"] = serializers.SerializerMethodField()
-
-        return super().to_representation(instance)
+            return super().to_representation(instance)
+        else:
+            # Fix: For PATCH/PUT responses, ensure streams are ordered
+            representation = super().to_representation(instance)
+            if "streams" in representation:
+                representation["streams"] = list(
+                    instance.streams.all()
+                    .order_by("channelstream__order")
+                    .values_list("id", flat=True)
+                )
+            return representation
 
     def get_logo(self, obj):
         return LogoSerializer(obj.logo).data