feat: add Celery/Redis task queue with feature flag support

Migrate background tasks from FastAPI BackgroundTasks to Celery with Redis
for persistent task queuing, retries, and scheduled jobs.

Key changes:
- Add Celery configuration with Redis broker/backend
- Create task dispatcher with USE_CELERY feature flag for gradual rollout
- Add Celery task wrappers for all background operations:
  - Marketplace imports
  - Letzshop historical imports
  - Product exports
  - Code quality scans
  - Test runs
  - Subscription scheduled tasks (via Celery Beat)
- Add celery_task_id column to job tables for Flower integration
- Add Flower dashboard link to admin background tasks page
- Update docker-compose.yml with worker, beat, and flower services
- Add Makefile targets: celery-worker, celery-beat, celery-dev, flower

When USE_CELERY=false (default), system falls back to FastAPI BackgroundTasks
for development without Redis dependency.

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

docker-compose.yml

@@ -1,13 +1,11 @@
 # docker-compose.yml
-version: '3.8'
-
 services:
   db:
     image: postgres:15
     restart: always
     environment:
       POSTGRES_DB: wizamart_db
-      POSTGRES_USER: ecommerce_user
+      POSTGRES_USER: wizamart_user
       POSTGRES_PASSWORD: secure_password
     volumes:
       - postgres_data:/var/lib/postgresql/data
@@ -24,7 +22,7 @@ services:
     image: redis:7-alpine
     restart: always
     ports:
-      - "6379:6379"
+      - "6380:6379"  # Use 6380 to avoid conflict with host Redis
     healthcheck:
       test: ["CMD", "redis-cli", "ping"]
       interval: 30s
@@ -34,12 +32,39 @@ services:
   api:
     build: .
     restart: always
+    profiles:
+      - full  # Only start with: docker compose --profile full up -d
     ports:
-      - "8000:8000"
+      - "8001:8000"  # Use 8001 to avoid conflict with local dev server
     environment:
       DATABASE_URL: postgresql://wizamart_user:secure_password@db:5432/wizamart_db
       JWT_SECRET_KEY: ${JWT_SECRET_KEY:-your-super-secret-key}
       REDIS_URL: redis://redis:6379/0
+      USE_CELERY: "true"
+    depends_on:
+      db:
+        condition: service_healthy
+      redis:
+        condition: service_healthy
+    volumes:
+      - ./logs:/app/logs
+      - ./uploads:/app/uploads
+    healthcheck:
+      test: ["CMD", "curl", "-f", "http://localhost:8000/health"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+
+  # Celery worker for processing background tasks
+  celery-worker:
+    build: .
+    restart: always
+    profiles:
+      - full  # Only start with: docker compose --profile full up -d
+    command: celery -A app.core.celery_config worker --loglevel=info -Q default,long_running,scheduled
+    environment:
+      DATABASE_URL: postgresql://wizamart_user:secure_password@db:5432/wizamart_db
+      REDIS_URL: redis://redis:6379/0
     depends_on:
       db:
         condition: service_healthy
@@ -47,11 +72,36 @@ services:
         condition: service_healthy
     volumes:
       - ./logs:/app/logs
-    healthcheck:
-      test: ["CMD", "curl", "-f", "http://localhost:8000/health"]
-      interval: 30s
-      timeout: 10s
-      retries: 3
+      - ./exports:/app/exports
+
+  # Celery beat for scheduled tasks
+  celery-beat:
+    build: .
+    restart: always
+    profiles:
+      - full  # Only start with: docker compose --profile full up -d
+    command: celery -A app.core.celery_config beat --loglevel=info
+    environment:
+      REDIS_URL: redis://redis:6379/0
+    depends_on:
+      redis:
+        condition: service_healthy
+
+  # Flower monitoring dashboard
+  flower:
+    build: .
+    restart: always
+    profiles:
+      - full  # Only start with: docker compose --profile full up -d
+    command: celery -A app.core.celery_config flower --port=5555
+    ports:
+      - "5555:5555"
+    environment:
+      REDIS_URL: redis://redis:6379/0
+      FLOWER_BASIC_AUTH: ${FLOWER_USER:-admin}:${FLOWER_PASSWORD:-changeme}
+    depends_on:
+      redis:
+        condition: service_healthy
 
 volumes:
   postgres_data: