Gallery wizard and a flatter admin

Galleries are built in a wizard with a story mode slide editor, a phone-frame preview, and an immersive playback view. The admin lost its cards: every page is left-aligned with one style of tabs and one visibility selector, the profile hub got category cards, and the top bar is the same everywhere. Artists can change their handle and the old one redirects. Storage went to 1.5GB and discovery moved behind sign-in.