M1 UI: shadcn + TeamUp design language

Initialize shadcn/ui (radix-nova, Tailwind v4) in client/ and rebuild the M1 interface
on the design language:
- Token layer recolored in index.css: light "calm command center" content surface,
  rationed indigo brand, the deep-indigo sidebar, the load-bearing seat-state triad
  (--color-seat-human slate / -open amber / -ai indigo) + teal "approved" / amber "held",
  Hanken Grotesk (variable) as the production font.
- App shell: deep-indigo sidebar (Board / Cartable / Org-chart-soon nav + sign out) on a
  light content area; StatusDot uses the seat-state tokens.
- LoginPage: Card-based sign-in / first-owner bootstrap, toast (sonner) errors.
- BoardPage: shadcn Card columns (backlog→in progress→in review→done), Badge task types,
  Select to move, Avatar/Assign-to-me, and the cartable panel — wired to the M1 API.
- Path alias @ -> src (tsconfig paths + vite); dropped baseUrl (deprecated in TS 6).

Components added via the shadcn CLI: button, card, badge, input, label, select,
separator, avatar, skeleton, sonner. Client `npm run build` is green (tsc + vite).
Still pending a live click-through.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/tsconfig.json

@@ -3,5 +3,10 @@
   "references": [
     { "path": "./tsconfig.app.json" },
     { "path": "./tsconfig.node.json" }
-  ]
+  ],
+  "compilerOptions": {
+    "paths": {
+      "@/*": ["./src/*"]
+    }
+  }
 }