Replace vanilla HTML with React + shadcn/ui + TailwindCSS scaffold

- Frontend: React 19 + Vite + TypeScript + TailwindCSS v4 + shadcn/ui
- Pre-installed shadcn/ui components: Button, Card, Input, Separator
- Multi-stage Dockerfile: build React client → serve with Express
- Server.js updated to serve built React SPA with API routes
- Sample landing page with shadcn/ui components demonstrating usage
- Path aliases (@/) configured in tsconfig + vite config
- components.json for easy `shadcn add <component>` usage

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

client/src/pages/Home.tsx

@@ -0,0 +1,85 @@
+import { Button } from '@/components/ui/button'
+import { Card, CardHeader, CardTitle, CardDescription, CardContent } from '@/components/ui/card'
+import { Separator } from '@/components/ui/separator'
+
+export default function HomePage() {
+  return (
+    <div className="min-h-screen bg-background">
+      {/* Header */}
+      <header className="border-b">
+        <div className="container mx-auto flex h-16 items-center justify-between px-4">
+          <h1 className="text-xl font-bold">Company Name</h1>
+          <nav className="flex items-center gap-4">
+            <Button variant="ghost">About</Button>
+            <Button variant="ghost">Contact</Button>
+            <Button>Get Started</Button>
+          </nav>
+        </div>
+      </header>
+
+      {/* Hero */}
+      <section className="container mx-auto px-4 py-24 text-center">
+        <h2 className="text-4xl font-bold tracking-tight sm:text-5xl">
+          Welcome to Your Company
+        </h2>
+        <p className="mx-auto mt-6 max-w-2xl text-lg text-muted-foreground">
+          This is your company website scaffold built with React, shadcn/ui, and TailwindCSS.
+          Start building your product here.
+        </p>
+        <div className="mt-10 flex justify-center gap-4">
+          <Button size="lg">Get Started</Button>
+          <Button size="lg" variant="outline">Learn More</Button>
+        </div>
+      </section>
+
+      <Separator />
+
+      {/* Features */}
+      <section className="container mx-auto px-4 py-16">
+        <h3 className="mb-8 text-center text-2xl font-bold">Features</h3>
+        <div className="grid gap-6 sm:grid-cols-2 lg:grid-cols-3">
+          <Card>
+            <CardHeader>
+              <CardTitle>Feature One</CardTitle>
+              <CardDescription>Description of the first feature.</CardDescription>
+            </CardHeader>
+            <CardContent>
+              <p className="text-sm text-muted-foreground">
+                Add details about this feature here.
+              </p>
+            </CardContent>
+          </Card>
+          <Card>
+            <CardHeader>
+              <CardTitle>Feature Two</CardTitle>
+              <CardDescription>Description of the second feature.</CardDescription>
+            </CardHeader>
+            <CardContent>
+              <p className="text-sm text-muted-foreground">
+                Add details about this feature here.
+              </p>
+            </CardContent>
+          </Card>
+          <Card>
+            <CardHeader>
+              <CardTitle>Feature Three</CardTitle>
+              <CardDescription>Description of the third feature.</CardDescription>
+            </CardHeader>
+            <CardContent>
+              <p className="text-sm text-muted-foreground">
+                Add details about this feature here.
+              </p>
+            </CardContent>
+          </Card>
+        </div>
+      </section>
+
+      {/* Footer */}
+      <footer className="border-t py-8">
+        <div className="container mx-auto px-4 text-center text-sm text-muted-foreground">
+          &copy; {new Date().getFullYear()} Company Name. All rights reserved.
+        </div>
+      </footer>
+    </div>
+  )
+}