feat(infra): 雲端就緒零影響改動 (compose overlay + healthcheck + env)

- docker-compose.yml：app healthcheck 改用 nc -z 127.0.0.1 9000 驗證 PHP-FPM port
- docker-compose.yml：移除 phpmyadmin、mailpit（開發工具不屬於正式服務）
- compose.override.yml：新增，含 phpmyadmin（8081）、mailpit（8025）port mapping
- .env.example：QUEUE_CONNECTION 預設改 redis；補充 FILESYSTEM_DISK、LOG_STACK、SESSION_DRIVER 雲端注意事項
- docs/STARTUP.md：新增「部署模式」章節，明確區分 VPS 與雲端 -f 指令

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

docker-compose.yml

@@ -38,11 +38,11 @@ services:
     
     # 健康檢查配置
     healthcheck:
-      test: ["CMD", "php", "-v"]  # 檢查 PHP 版本確認服務正常
-      interval: 30s  # 每30秒檢查一次
-      timeout: 10s  # 超時時間10秒
-      retries: 3  # 重試3次
-      start_period: 40s  # 容器啟動後40秒開始檢查
+      test: ["CMD-SHELL", "nc -z 127.0.0.1 9000 || exit 1"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 40s
 
   nginx:
     image: nginx:alpine
@@ -109,21 +109,6 @@ services:
     ports:
       - "127.0.0.1:3306:3306" # 只綁 localhost，不對外
 
-  phpmyadmin:
-    image: phpmyadmin/phpmyadmin
-    container_name: cfdive-phpmyadmin
-    restart: unless-stopped
-    environment:
-      PMA_HOST: db
-      PMA_PORT: 3306
-      PMA_USER: ${DB_USERNAME:-cfdiveuser}
-      PMA_PASSWORD: ${DB_PASSWORD}
-      MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
-    networks:
-      - cfdive-network
-    depends_on:
-      db:
-        condition: service_healthy
 
   queue-worker:
     image: cfdive-platform
@@ -146,12 +131,6 @@ services:
       app:
         condition: service_healthy
 
-  mailpit:
-    image: axllent/mailpit
-    container_name: cfdive-mailpit
-    restart: unless-stopped
-    networks:
-      - cfdive-network
 
   redis:
     image: redis:alpine