Moved unique Legion character backstories to a new CharacterBackstories_Legion.xml file and removed them from BackstoryDefs_Legion.xml. Added Unique_PawnKinds_Legion.xml to define unique pawn kinds for Caesar, Lanius, Lucius, Vulpes, and Aurelius, and updated CharacterDefs_Legion.xml and FCP_Legion.xml to use these new pawn kinds. Cleaned up PawnKinds.xml by removing unique Legion pawn kinds from the base file.
