Add Docker Compose project scaffold

Sets up the full monorepo structure with:
- Multi-stage Dockerfile (client-build + production stages)
- docker-compose.yml for production, docker-compose.dev.yml overlay for development
- Express server (port 3000) with pg pool, health route, and SPA static file serving
- React 18 + Vite client with react-router-dom v6, nav bar, and placeholder page components
- .env.example with PostgreSQL and app config
- Empty db/migrations/ directory for future migrations
- CLAUDE.md updated with development workflow commands

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

server/src/index.js

@@ -0,0 +1,27 @@
+require('dotenv').config();
+const express = require('express');
+const cors = require('cors');
+const path = require('path');
+const healthRouter = require('./routes/health');
+
+const app = express();
+const PORT = process.env.PORT || 3000;
+
+app.use(cors());
+app.use(express.json());
+
+// API routes
+app.use('/api', healthRouter);
+
+// Serve static client files in production
+const clientDist = path.join(__dirname, '../../client/dist');
+app.use(express.static(clientDist));
+
+// SPA fallback — send index.html for any unmatched route
+app.get('*', (req, res) => {
+  res.sendFile(path.join(clientDist, 'index.html'));
+});
+
+app.listen(PORT, () => {
+  console.log(`Server running on port ${PORT}`);
+});