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>

Dockerfile

@@ -1,3 +1,15 @@
+FROM node:20-alpine AS builder
+
+WORKDIR /app/client
+
+# Install client dependencies and build
+COPY client/package*.json ./
+RUN npm install
+
+COPY client/ ./
+RUN npm run build
+
+# --- Production stage ---
 FROM node:20-alpine
 
 ARG SOURCE_COMMIT=unknown
@@ -5,15 +17,17 @@ ARG APP_VERSION=1.0.0
 
 WORKDIR /app
 
-# Install curl for healthcheck
 RUN apk add --no-cache curl
 
-# Copy package files first for layer caching
+# Install server dependencies
 COPY package*.json ./
 RUN npm install --production
 
-# Copy app code
-COPY . .
+# Copy server code
+COPY server.js ./
+
+# Copy built React app from builder
+COPY --from=builder /app/client/dist ./client/dist
 
 ENV GIT_COMMIT=${SOURCE_COMMIT} \
     APP_VERSION=${APP_VERSION}