SAN FRANCISCO — Beating the Fire in their regular-season opener Saturday was a good sign for the Sky.Sure, the Fire are an expansion franchise that won’t sniff the playoffs this season, but you don’t scoff at any victories if you’re the Sky. Not when you scraped together only 10 of them last season. Not when four of your top eight players were watching in street clothes.You can earn a few stripes beating a bad team while short-handed, but you re…