fix: don't use BUILD_HASH build arg until needed, busts cache otherwise

Dockerfile

@@ -38,7 +38,6 @@ ARG USE_OLLAMA
 ARG USE_CUDA_VER
 ARG USE_EMBEDDING_MODEL
 ARG USE_RERANKING_MODEL
-ARG BUILD_HASH
 ARG UID
 ARG GID
 
@@ -154,6 +153,7 @@ HEALTHCHECK CMD curl --silent --fail http://localhost:8080/health | jq -e '.stat
 
 USER $UID:$GID
 
+ARG BUILD_HASH
 ENV WEBUI_BUILD_VERSION=${BUILD_HASH}
 
 CMD [ "bash", "start.sh"]