Support DomeLight automatic format

When the DomeLight has a texture, its default value for the texture format is "automatic". This isn't supported at the moment and defaults to arnold default value which is "angular". We might want to consider changing this value to latlong, or eventually to support the automatic mode properly

Start by tracing how DomeLight texture formats are handled and compare the current automatic fallback with Arnold's angular default. The issue presents two possible outcomes—using latlong or supporting automatic mode properly—so completion requires first deciding which behavior is intended, then verifying that automatic no longer silently becomes angular.

Written by the indexing model from the issue text.