feat: keep every brick by brick save before it is split into models

The save is stored as the client sent it in the new ugc_unsplit table, and each model split from it points back to it (ugc.unsplit_id), so the whole build can be looked at or restored later. A save is kept while any model split from it exists: deleting models removes saves no model points to any more, and deleting a character removes its saves.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dDatabase/GameDatabase/MySQL/MySQLDatabase.cpp

@@ -107,6 +107,7 @@ void MySQLDatabase::DeleteCharacter(const LWOOBJID characterId) {
 	ExecuteDelete("DELETE FROM properties_contents WHERE property_id IN (SELECT id FROM properties WHERE owner_id=?);", characterId);
 	ExecuteDelete("DELETE FROM properties WHERE owner_id=?;", characterId);
 	ExecuteDelete("DELETE FROM ugc WHERE character_id=?;", characterId);
+	ExecuteDelete("DELETE FROM ugc_unsplit WHERE character_id=?;", characterId);
 	ExecuteDelete("DELETE FROM activity_log WHERE character_id=?;", characterId);
 	ExecuteDelete("DELETE FROM mail WHERE receiver_id=?;", characterId);
 	ExecuteDelete("DELETE FROM ignore_list WHERE player_id=? OR ignored_player_id=?;", characterId, characterId);