feat: add Sentry, Cloudflare R2, and CloudFlare CDN integrations

Production quick wins for improved observability and scalability:

Sentry Error Tracking:
- Add sentry-sdk[fastapi] dependency
- Initialize Sentry in main.py with FastAPI/SQLAlchemy integrations
- Add Celery integration for background task error tracking
- Feature-flagged via SENTRY_DSN (disabled when empty)

Cloudflare R2 Storage:
- Add boto3 dependency for S3-compatible API
- Create storage_service.py with StorageBackend abstraction
- LocalStorageBackend for development (default)
- R2StorageBackend for production cloud storage
- Feature-flagged via STORAGE_BACKEND setting

CloudFlare CDN/Proxy:
- Create middleware/cloudflare.py for CF header handling
- Extract real client IP from CF-Connecting-IP
- Support CF-IPCountry for geo features
- Feature-flagged via CLOUDFLARE_ENABLED setting

Documentation:
- Add docs/deployment/cloudflare.md setup guide
- Update infrastructure.md with dev vs prod requirements
- Add enterprise upgrade checklist for scaling beyond 1000 users
- Update installation.md with new environment variables

All features are optional and disabled by default for development.

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

docs/getting-started/installation.md

@@ -236,6 +236,31 @@ pytest -m integration
 | `FLOWER_URL` | Flower dashboard URL | `http://localhost:5555` | ❌ |
 | `FLOWER_PASSWORD` | Flower authentication password | `changeme` | ❌ |
 
+### Sentry Error Tracking
+
+| Variable | Description | Default | Required |
+|----------|-------------|---------|----------|
+| `SENTRY_DSN` | Sentry DSN (leave empty to disable) | - | ❌ |
+| `SENTRY_ENVIRONMENT` | Environment name | `development` | ❌ |
+| `SENTRY_TRACES_SAMPLE_RATE` | Performance tracing rate (0.0-1.0) | `0.1` | ❌ |
+
+### Cloudflare R2 Storage
+
+| Variable | Description | Default | Required |
+|----------|-------------|---------|----------|
+| `STORAGE_BACKEND` | Storage backend (`local` or `r2`) | `local` | ❌ |
+| `R2_ACCOUNT_ID` | Cloudflare account ID | - | ❌ (if r2) |
+| `R2_ACCESS_KEY_ID` | R2 access key | - | ❌ (if r2) |
+| `R2_SECRET_ACCESS_KEY` | R2 secret key | - | ❌ (if r2) |
+| `R2_BUCKET_NAME` | R2 bucket name | `wizamart-media` | ❌ |
+| `R2_PUBLIC_URL` | Custom public URL for R2 | - | ❌ |
+
+### CloudFlare CDN
+
+| Variable | Description | Default | Required |
+|----------|-------------|---------|----------|
+| `CLOUDFLARE_ENABLED` | Enable CloudFlare header handling | `false` | ❌ |
+
 ### Stripe Billing
 
 | Variable | Description | Default | Required |