chore: scaffold Bun + React + shadcn project

bun init --react=shadcn, with the demo API routes removed since this app
has no backend. Adds project invariants to CLAUDE.md and a smoke test
proving the domain layer imports with no DOM.

src/index.css

@@ -0,0 +1,28 @@
+@import "../styles/globals.css";
+
+@layer base {
+  :root {
+    @apply font-sans;
+  }
+
+  body {
+    @apply grid place-items-center min-w-[320px] min-h-screen relative m-0 bg-background text-foreground;
+  }
+}
+
+@keyframes spin {
+  from {
+    transform: rotate(0);
+  }
+  to {
+    transform: rotate(360deg);
+  }
+}
+
+@media (prefers-reduced-motion) {
+  *,
+  ::before,
+  ::after {
+    animation: none !important;
+  }
+}