Tuist-styled login and new dashboard shell with Hive logo

The login page and dashboard chrome now use a Tuist-style design: a centered 50x50 Hive honeycomb logo, heading-medium title, body-small subtitle, and large blurred purple oklch gradient accents in the background. The dashboard also gets a new shared Layouts module with a headerbar, sidebar, and content area, plus the Hive logo wired in as the headerbar logo and favicon. The overview page is simplified to a title, subtitle, and Getting started card instead of the earlier placeholder hero and metric grid. Sources: https://github.com/tuist/hive/commit/66de972, https://github.com/tuist/hive/commit/b29e645