Federal Bureau of Investigation agents swarmed a Grass Valley apartment early Tuesday, seizing two luxury vehicles and reportedly detaining one woman. But a spokeswoman at the FBI’s Sacramento office would confirm only that the bureau “did have some law enforcement activity” in Nevada County. She declined to comment as to whether any arrests were made or were pending, referring questions to the U.S. Attorney’s office. A spokeswoman from that office did not return calls for comment, and no criminal cases involving Nevada County residents were listed as having been filed in U.S. District Court in Sacramento this week. Federal agents …