Initial commit: Børnetime app scaffold

FastAPI + Celery + Svelte app for English→Danish video translation
with voice cloning. Includes diarization, STT, translation, TTS,
and audio mixing pipeline.

backend/app/tasks/celery_app.py

@@ -0,0 +1,19 @@
+from celery import Celery
+from ..config import settings
+
+celery_app = Celery(
+    "bornetime",
+    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,
+    task_acks_late=True,
+    worker_prefetch_multiplier=1,
+)