By EMILI VESILIND The relaxed, breezy atmosphere of Patricia Assui Reed’s Matriark boutique in Sag Harbor, N.Y., could feel accidental—as though a stylish, jet-setting friend decided to open her Victorian home as a weekend shop filled with alluring fashion, jewelry, accessories, and home wares. But this easygoing ambience was thoughtfully orchestrated by Patricia Assui Reed, who, before moving to the Hamptons with her…