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>

CLAUDE.md

@@ -24,3 +24,25 @@ td session --new         # force a new session in the same terminal context
 ```
 
 Task state is stored in `.todos/issues.db` (SQLite).
+
+## Development
+
+**Run production stack (Docker):**
+```bash
+docker compose up
+```
+
+**Run development stack with live reload (Docker):**
+```bash
+docker compose -f docker-compose.yml -f docker-compose.dev.yml up
+```
+
+**Frontend only (Vite dev server):**
+```bash
+cd client && npm install && npm run dev
+```
+
+**Backend only (nodemon):**
+```bash
+cd server && npm install && npm run dev
+```