Add FastAPI application, API endpoints, Celery workers, and Docker configuration

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

backend/app/workers/celery_app.py

@@ -0,0 +1,51 @@
+"""
+Celery application for background email processing tasks.
+"""
+from celery import Celery
+from celery.schedules import crontab
+import logging
+
+from app.core.config import settings
+
+logger = logging.getLogger(__name__)
+
+# Create Celery app
+celery_app = Celery(
+    "pop3_forwarder",
+    broker=settings.CELERY_BROKER_URL,
+    backend=settings.CELERY_RESULT_BACKEND,
+    include=["app.workers.tasks"]
+)
+
+# Celery configuration
+celery_app.conf.update(
+    task_serializer="json",
+    accept_content=["json"],
+    result_serializer="json",
+    timezone="UTC",
+    enable_utc=True,
+    task_track_started=True,
+    task_time_limit=30 * 60,  # 30 minutes
+    task_soft_time_limit=25 * 60,  # 25 minutes
+    worker_prefetch_multiplier=1,
+    worker_max_tasks_per_child=1000,
+)
+
+# Periodic tasks schedule
+celery_app.conf.beat_schedule = {
+    "process-all-mail-accounts": {
+        "task": "app.workers.tasks.process_all_enabled_accounts",
+        "schedule": crontab(minute="*/5"),  # Every 5 minutes
+    },
+    "cleanup-old-logs": {
+        "task": "app.workers.tasks.cleanup_old_logs",
+        "schedule": crontab(hour=3, minute=0),  # Daily at 3 AM
+    },
+}
+
+
+@celery_app.task(bind=True)
+def debug_task(self):
+    """Debug task to test Celery"""
+    logger.info(f"Request: {self.request!r}")
+    return "Celery is working!"