feat: add React application shell with dark mode UI

Create the minimal React application structure for Mission Control:

Entry Points:
- index.html: Dark mode root (class="dark", bg-surface body)
- src/main.tsx: React 19 createRoot with StrictMode

Application Shell:
- src/App.tsx: Initial landing with "THE ONE THING" placeholder
  - Uses Framer Motion for subtle fade-in animation
  - Centered layout with Mission Control branding
  - Surfaces the core UX principle: "What should you be doing right now?"

Styling:
- src/styles.css: Tailwind directives + custom scrollbar styling
  - Dark scrollbars (zinc-700 thumb, transparent track)
  - .no-select utility for draggable elements

The shell is deliberately minimal - it will evolve as beads integration
(bd-28q) and dashboard components (bd-30f) are implemented.

src/App.tsx

@@ -0,0 +1,28 @@
+import { motion } from "framer-motion";
+
+function App() {
+  return (
+    <div className="flex min-h-screen flex-col items-center justify-center p-8">
+      <motion.div
+        initial={{ opacity: 0, scale: 0.9 }}
+        animate={{ opacity: 1, scale: 1 }}
+        transition={{ duration: 0.3 }}
+        className="text-center"
+      >
+        <h1 className="mb-4 text-4xl font-bold tracking-tight">
+          Mission Control
+        </h1>
+        <p className="mb-8 text-xl text-zinc-400">
+          What should you be doing right now?
+        </p>
+        <div className="rounded-xl border border-zinc-700 bg-surface-raised p-8">
+          <p className="text-lg text-zinc-300">
+            THE ONE THING will appear here
+          </p>
+        </div>
+      </motion.div>
+    </div>
+  );
+}
+
+export default App;

src/main.tsx

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+import React from "react";
+import ReactDOM from "react-dom/client";
+import App from "./App";
+import "./styles.css";
+
+ReactDOM.createRoot(document.getElementById("root")!).render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>
+);

src/styles.css

@@ -0,0 +1,27 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+/* Custom scrollbar for dark mode */
+::-webkit-scrollbar {
+  width: 8px;
+  height: 8px;
+}
+
+::-webkit-scrollbar-track {
+  background: transparent;
+}
+
+::-webkit-scrollbar-thumb {
+  background: #3f3f46;
+  border-radius: 4px;
+}
+
+::-webkit-scrollbar-thumb:hover {
+  background: #52525b;
+}
+
+/* Prevent text selection on draggable items */
+.no-select {
+  user-select: none;
+}