fix: add persistent huggingface cache volume for worker

Prevents re-downloading Whisper model on container recreate.
Also switched to whisper medium (large-v3 OOM on 8GB VRAM with Ollama).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -22,6 +22,7 @@ services:
     volumes:
       - uploads:/app/uploads
       - exports:/app/exports
+      - huggingface_cache:/root/.cache/huggingface
     depends_on:
       db:
         condition: service_healthy
@@ -78,3 +79,4 @@ volumes:
   pgdata:
   uploads:
   exports:
+  huggingface_cache: