feat(phase-4): Complete scheduling and automation system

- Add Celery worker with 5 scheduled tasks (Beat)
- Create ContentScheduler for optimal posting times
- Add calendar endpoints for scheduled posts management
- Implement Telegram notification service
- Add notification API with setup guide

Celery Beat Schedule:
- check_scheduled_posts: Every minute
- generate_daily_content: Daily at 6 AM
- sync_interactions: Every 15 minutes
- send_daily_summary: Daily at 9 PM
- cleanup_old_data: Weekly on Sundays

New endpoints:
- GET /api/calendar/posts/scheduled - List scheduled posts
- GET /api/calendar/posts/view - Calendar view
- GET /api/calendar/posts/slots - Available time slots
- POST /api/calendar/posts/{id}/schedule - Schedule post
- POST /api/calendar/posts/{id}/publish-now - Publish immediately
- GET /api/notifications/status - Check notification config
- POST /api/notifications/test - Send test notification
- GET /api/notifications/setup-guide - Configuration guide

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

app/worker/__init__.py

@@ -0,0 +1,7 @@
+"""
+Celery worker module for background tasks.
+"""
+
+from app.worker.celery_app import celery_app
+
+__all__ = ["celery_app"]