Theme system with 5 color presets (Slate, Emerald, Violet, Amber, Rose)
and light/dark/system mode. User menu in sidebar with theme picker and
sign out. Login page uses standalone dark branded styling with autofill
override. Auth persists in sessionStorage across refreshes.
Sets up the admin frontend with login page, auth guard, API client, Zustand
auth store, and all shadcn/ui components. Vite proxies /v1 to backend in dev.
