build(docker): speed up on CPU

Dockerfile

@@ -12,7 +12,7 @@ COPY requirements.txt ./
 RUN --mount=from=ghcr.io/astral-sh/uv:0.9.5,source=/uv,target=/bin/uv \
     --mount=type=cache,target=/root/.cache/uv \
     --mount=type=bind,source=requirements.txt,target=requirements.txt \
-    uv pip install --system -r requirements.txt
+    UV_TORCH_BACKEND='cpu' uv pip install --system -r requirements.txt
 
 COPY src/ ./src/