Initial scaffold: React 19 + Vite + TypeScript + Tailwind CSS v4 + Storybook 10

Design system and component library for the Research Synthesiser. Includes:
- Tailwind CSS v4 with @theme-based design tokens from the existing synthesiser
- Storybook 10.4 with MCP, a11y, docs, and vitest addons
- ESLint + Prettier with Tailwind class sorting
- Button component as pipeline validation
- CLAUDE.md with project principles and conventions
- ARCHITECTURE.md as living architecture document
- Penpot and Storybook MCP server configuration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/App.tsx

@@ -0,0 +1,16 @@
+function App() {
+  return (
+    <div className="min-h-screen bg-bg text-text">
+      <header className="bg-surface border-b border-border px-6 py-3">
+        <h1 className="text-lg font-semibold">SDC Design System</h1>
+      </header>
+      <main className="p-6">
+        <p className="text-text-secondary">
+          Component library for the Research Synthesiser.
+        </p>
+      </main>
+    </div>
+  )
+}
+
+export default App