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/celery_app.py

@@ -0,0 +1,76 @@
+"""
+Celery application configuration.
+"""
+
+from celery import Celery
+from celery.schedules import crontab
+
+from app.core.config import settings
+
+
+# Create Celery app
+celery_app = Celery(
+    "social_automation",
+    broker=settings.REDIS_URL,
+    backend=settings.REDIS_URL,
+    include=[
+        "app.worker.tasks",
+    ]
+)
+
+# Celery configuration
+celery_app.conf.update(
+    # Serialization
+    task_serializer="json",
+    accept_content=["json"],
+    result_serializer="json",
+
+    # Timezone
+    timezone="America/Tijuana",
+    enable_utc=True,
+
+    # Task settings
+    task_track_started=True,
+    task_time_limit=300,  # 5 minutes max per task
+    task_soft_time_limit=240,  # Soft limit 4 minutes
+
+    # Result backend settings
+    result_expires=86400,  # Results expire after 24 hours
+
+    # Worker settings
+    worker_prefetch_multiplier=1,
+    worker_concurrency=4,
+
+    # Beat schedule for periodic tasks
+    beat_schedule={
+        # Check and publish scheduled posts every minute
+        "check-scheduled-posts": {
+            "task": "app.worker.tasks.check_scheduled_posts",
+            "schedule": 60.0,  # Every minute
+        },
+
+        # Generate daily content at 6 AM
+        "generate-daily-content": {
+            "task": "app.worker.tasks.generate_daily_content",
+            "schedule": crontab(hour=6, minute=0),
+        },
+
+        # Sync interactions every 15 minutes
+        "sync-interactions": {
+            "task": "app.worker.tasks.sync_interactions",
+            "schedule": crontab(minute="*/15"),
+        },
+
+        # Send daily summary at 9 PM
+        "send-daily-summary": {
+            "task": "app.worker.tasks.send_daily_summary",
+            "schedule": crontab(hour=21, minute=0),
+        },
+
+        # Cleanup old data weekly
+        "cleanup-old-data": {
+            "task": "app.worker.tasks.cleanup_old_data",
+            "schedule": crontab(hour=3, minute=0, day_of_week=0),  # Sunday 3 AM
+        },
+    },
+)