feat: add production deployment config

- Add docker-compose.prod.yml and Caddyfile for Caddy reverse proxy
- Add production stages to frontend Dockerfile (nginx for static files)
- Fix monorepo package exports for production builds (dist/src paths)
- Add CORS_ORIGIN env var for cross-origin config
- Add Better Auth baseURL, cookie domain, and trusted origins from env
- Use VITE_API_URL for API calls in auth-client and play route
- Add credentials: include for cross-origin fetch requests
- Remove unused users table from schema

Caddyfile

@@ -0,0 +1,11 @@
+lilastudy.com {
+	reverse_proxy web:80
+}
+
+api.lilastudy.com {
+	reverse_proxy api:3000
+}
+
+git.lilastudy.com {
+	reverse_proxy forgejo:3000
+}