SAN FRANCISCO Feb. 14 — Gay and lesbian couples from across the country answered this city's Valentine's Day invitation to wed in an unprecedented spree of same-sex marriages that has challenged California law and sent conservative groups scrambling for court intervention. About 500 people lined up Saturday morning outside City Hall to secure marriage licenses and then take each other as "spouse for life" in brief vows that have given San Francisco's seat of government the feel of a Las Vegas wedding chapel. As passing drivers honked and strangers passed out roses, those waiting hours in line cheered couples who...