feat: add Docker Compose development stack (#24)

- Add docker-compose.yml with PostgreSQL 15 and Redis 7
- Add health checks for both services
- Add optional dev tools (Adminer, RedisInsight) via 'tools' profile
- Create .env.example with all configuration variables
- Update README.md with Docker setup documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,72 @@
+version: "3.8"
+
+services:
+  postgres:
+    image: postgres:15
+    container_name: polymarket-postgres
+    ports:
+      - "${POSTGRES_PORT:-5432}:5432"
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    environment:
+      POSTGRES_DB: ${POSTGRES_DB:-polymarket_tracker}
+      POSTGRES_USER: ${POSTGRES_USER:-tracker}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-dev_password}
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-tracker} -d ${POSTGRES_DB:-polymarket_tracker}"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+      start_period: 10s
+    restart: unless-stopped
+
+  redis:
+    image: redis:7
+    container_name: polymarket-redis
+    ports:
+      - "${REDIS_PORT:-6379}:6379"
+    volumes:
+      - redis_data:/data
+    command: redis-server --appendonly yes
+    healthcheck:
+      test: ["CMD", "redis-cli", "ping"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+      start_period: 5s
+    restart: unless-stopped
+
+  # Optional development tools - use with: docker compose --profile tools up
+  adminer:
+    image: adminer:latest
+    container_name: polymarket-adminer
+    ports:
+      - "${ADMINER_PORT:-8080}:8080"
+    depends_on:
+      postgres:
+        condition: service_healthy
+    profiles:
+      - tools
+    restart: unless-stopped
+
+  redis-insight:
+    image: redis/redisinsight:latest
+    container_name: polymarket-redis-insight
+    ports:
+      - "${REDIS_INSIGHT_PORT:-5540}:5540"
+    volumes:
+      - redis_insight_data:/data
+    depends_on:
+      redis:
+        condition: service_healthy
+    profiles:
+      - tools
+    restart: unless-stopped
+
+volumes:
+  postgres_data:
+    driver: local
+  redis_data:
+    driver: local
+  redis_insight_data:
+    driver: local