feat: Docker, docker-compose, and deployment config (Task 13)

- Dockerfile: two-stage build (builder installs all deps + vite build; runtime copies dist + server)
- docker-compose.yml: 127.0.0.1:3004:8080, named volume for SQLite, env var interpolation
- .env.example: all required environment variables documented
- .dockerignore: exclude node_modules, dist, data, .env from build context
- vite.config.ts: outDir → ../client/dist, /api proxy to :3001 for dev
- .gitignore: remove Docker entries (files should be tracked for deployment)

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

vite.config.ts

@@ -5,7 +5,7 @@ export default defineConfig({
   root: 'client',
   plugins: [react()],
   build: {
-    outDir: 'dist',
+    outDir: '../client/dist',
     emptyOutDir: true,
   },
   server: {