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>

app/core/celery_config.py

@@ -7,16 +7,33 @@ It includes:
 - Task routing to separate queues (default, long_running, scheduled)
 - Celery Beat schedule for periodic tasks
 - Task retry policies
+- Sentry integration for error tracking
 """
 
 import os
 
+import sentry_sdk
 from celery import Celery
 from celery.schedules import crontab
+from sentry_sdk.integrations.celery import CeleryIntegration
 
 # Redis URL from environment or default
 REDIS_URL = os.getenv("REDIS_URL", "redis://localhost:6379/0")
 
+# =============================================================================
+# SENTRY INITIALIZATION FOR CELERY WORKERS
+# =============================================================================
+# Celery workers run in separate processes, so Sentry must be initialized here too
+SENTRY_DSN = os.getenv("SENTRY_DSN")
+if SENTRY_DSN:
+    sentry_sdk.init(
+        dsn=SENTRY_DSN,
+        environment=os.getenv("SENTRY_ENVIRONMENT", "development"),
+        traces_sample_rate=float(os.getenv("SENTRY_TRACES_SAMPLE_RATE", "0.1")),
+        integrations=[CeleryIntegration()],
+        send_default_pii=True,
+    )
+
 # Create Celery application
 celery_app = Celery(
     "wizamart",