♻️(backend) rename convert_markdown to convert (#1114)

Renamed the `convert_markdown` method to `convert` to prepare for an
all-purpose conversion endpoint, enabling support for multiple formats
and simplifying future extension.

Signed-off-by: Stephan Meijer <me@stephanmeijer.com>

src/backend/core/api/serializers.py

@@ -408,9 +408,7 @@ class ServerCreateDocumentSerializer(serializers.Serializer):
             language = user.language or language
 
         try:
-            document_content = YdocConverter().convert_markdown(
-                validated_data["content"]
-            )
+            document_content = YdocConverter().convert(validated_data["content"])
         except ConversionError as err:
             raise serializers.ValidationError(
                 {"content": ["Could not convert content"]}