docs: update documentation with Celery/Redis and Makefile changes

- Update Makefile help sections with correct target names (platform-install)
- Add Celery infrastructure section to background-tasks.md
- Update installation.md with Celery setup instructions and environment vars
- Update index.md with comprehensive development commands including Celery
- Add Flower monitoring and task queue commands to docs

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

docs/architecture/background-tasks.md

@@ -4,6 +4,77 @@
 
 This document defines the harmonized architecture for all background tasks in the application. Background tasks are long-running operations that execute asynchronously, allowing users to continue browsing while the task completes.
 
+## Task Queue Infrastructure
+
+Wizamart uses **Celery with Redis** for production-grade background task processing:
+
+| Component | Purpose | Port |
+|-----------|---------|------|
+| **Celery Worker** | Executes background tasks | - |
+| **Celery Beat** | Scheduled task scheduler | - |
+| **Redis** | Message broker & result backend | 6379 |
+| **Flower** | Web-based task monitoring | 5555 |
+
+### Configuration
+
+```bash
+# Environment variables (.env)
+REDIS_URL=redis://localhost:6379/0
+USE_CELERY=true                    # false = use FastAPI BackgroundTasks
+FLOWER_URL=http://localhost:5555
+FLOWER_PASSWORD=changeme
+```
+
+### Running Celery
+
+```bash
+# Start Redis
+docker compose up -d redis
+
+# Start Celery worker (processes tasks)
+make celery-worker
+
+# Start Celery beat (scheduled tasks)
+make celery-beat
+
+# Start both together (development)
+make celery-dev
+
+# Start Flower monitoring
+make flower
+```
+
+### Feature Flag: USE_CELERY
+
+The system supports gradual migration via the `USE_CELERY` feature flag:
+
+- **`USE_CELERY=false` (default)**: Uses FastAPI's `BackgroundTasks` for immediate execution without Redis dependency. Suitable for development.
+- **`USE_CELERY=true`**: Routes tasks through Celery for persistent queuing, retries, and scheduling. Required for production.
+
+### Task Routing
+
+Tasks are routed to queues based on their characteristics:
+
+| Queue | Tasks | Characteristics |
+|-------|-------|-----------------|
+| `default` | Product exports | Fast, non-blocking |
+| `long_running` | Imports, code quality scans, tests | May take 10+ minutes |
+| `scheduled` | Subscription maintenance | Triggered by Celery Beat |
+
+### Celery Task ID Tracking
+
+All background job models include a `celery_task_id` field for cross-referencing with Flower:
+
+```python
+class MarketplaceImportJob(Base):
+    celery_task_id = Column(String(255), nullable=True)
+```
+
+This enables:
+- Deep linking to Flower for task details
+- Task cancellation via Flower API
+- Correlation between database records and Celery events
+
 ## Current State Analysis
 
 | Task Type | Database Model | Status Values | Tracked in BG Tasks Page |