feat: add Docker deployment and application configuration

Add package declarations across the Go scaffold, YAML configuration loading and validation, and a minimal API entry point.

Add development and production Compose files, a multi-stage Docker image, configuration template, and Make targets. Remove the directory scaffolding script.

deploy/docker-compose.prod.yml

@@ -0,0 +1,15 @@
+services:
+  backend:
+    build:
+      context: ..
+      dockerfile: Dockerfile
+    image: ${ROBOT_MARKET_IMAGE:-robot-market-backend:latest}
+    environment:
+      CONFIG_FILE: /etc/robot-market/config.yaml
+    volumes:
+      - ${CONFIG_FILE:-../configs/config.example.yaml}:/etc/robot-market/config.yaml:ro
+    ports:
+      - "${APP_PORT:-8080}:8080"
+    extra_hosts:
+      - "host.docker.internal:host-gateway"
+    restart: unless-stopped