feat: Celery setup and transcription task — Whisper + FFmpeg pipeline

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/tasks/celery_app.py

@@ -0,0 +1,27 @@
+from celery import Celery
+from celery.schedules import crontab
+
+from app.config import settings
+
+celery_app = Celery(
+    "meeting_protocol",
+    broker=settings.redis_url,
+    backend=settings.redis_url,
+)
+
+celery_app.conf.update(
+    task_serializer="json",
+    accept_content=["json"],
+    result_serializer="json",
+    timezone="UTC",
+    enable_utc=True,
+    task_track_started=True,
+    beat_schedule={
+        "cleanup-old-data": {
+            "task": "app.tasks.cleanup.cleanup_old_data",
+            "schedule": crontab(hour=3, minute=0),
+        },
+    },
+)
+
+celery_app.autodiscover_tasks(["app.tasks"])