On a summer’s day, the 30,000 islands that bask between the island-city of Stockholm and the Baltic Sea are alive with sun-seekers and merrymakers. The islands and islets are dotted with red-painted cottages and waterside saunas. Every shore has a dock and a boat or two. The optimistic blue-and-gold flags of Sweden flutter from poles, and kids splash along the rocky shorelines. White-sailed yachts…