Redesigned dashboard layout and login screen

The dashboard and login pages now share an Atlas-style shell: a dedicated dashboard layout with a headerbar, sidebar, and content area, plus the Hive honeycomb logo in the header, favicon, and login frame. The login page has been redesigned to match the Tuist auth experience with refined typography, a centered 50x50 logo, large blurred purple gradients, and a responsive frame that fits small screens.