Adds the styling foundation for the UI redesign (vibe-kanban / Magentic-UI /
Langflow references): Tailwind CSS + shadcn/ui primitives, HSL design tokens
(index.css) ported from theme.css, @/ alias, and the App.tsx Board|Pipeline tabs
shell. Extends StateResponse with the backend's existing stages[] for the Board.
theme.css kept transiently until components migrate to Tailwind. No backend
changes. Component fan-out (Board, MapNode, TaskDrawer, TopBar) follows.
