chore: import upstream snapshot with attribution

docker/Dockerfile.cpu

@@ -0,0 +1,25 @@
+ARG PYTHON_VERSION=3.11
+FROM python:${PYTHON_VERSION}-slim
+
+ARG LEANN_VERSION=0.3.6
+
+ENV PIP_NO_CACHE_DIR=1 \
+    PIP_DISABLE_PIP_VERSION_CHECK=1 \
+    PIP_ROOT_USER_ACTION=ignore \
+    PIP_INDEX_URL=https://download.pytorch.org/whl/cpu \
+    PIP_EXTRA_INDEX_URL=https://pypi.org/simple
+
+# Keep runtime image minimal while ensuring common C++ runtime libs are present.
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+        libgomp1 \
+        libstdc++6 \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN python -m pip install --upgrade pip \
+    && pip install --prefer-binary "leann==${LEANN_VERSION}" \
+    && python -c "import leann; import leann_backend_hnsw; import leann_backend_diskann"
+
+WORKDIR /workspace
+
+CMD ["python", "-c", "import leann; print('LEANN installed and importable (CPU image).')"]