fix(docker): rewrite agentsmirror lock URLs and refresh numpy

uv.lock uses uv.agentsmirror.com paths that the old sed rules never matched,
which could install corrupted wheels from cache. Rewrite to Tsinghua mirrors,
force-refresh numpy/mediapipe, and verify numpy imports during the image build.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/Dockerfile

@@ -51,11 +51,11 @@ COPY alembic ./alembic/
 # 离线批处理 / demo 直调 algorithm_subprocesses/5.15/main.py（含 weights/）
 COPY algorithm_subprocesses ./algorithm_subprocesses/
 
-# uv.lock pins full download URLs. Rewrite to mainland-accessible mirrors (same paths / hashes).
+# uv.lock pins uv.agentsmirror.com artifact URLs. Rewrite to mainland mirrors (same /packages/... paths).
 # PyPI: Tsinghua  |  PyTorch wheel index: 南大 (syncs download.pytorch.org / download-r2)
 RUN sed -i \
-  -e 's|https://files.pythonhosted.org|https://pypi.tuna.tsinghua.edu.cn|g' \
-  -e 's|https://pypi.org/simple|https://pypi.tuna.tsinghua.edu.cn/simple|g' \
+  -e 's|https://uv.agentsmirror.com/pypi/files/files.pythonhosted.org|https://pypi.tuna.tsinghua.edu.cn|g' \
+  -e 's|https://uv.agentsmirror.com/pypi/simple|https://pypi.tuna.tsinghua.edu.cn/simple|g' \
   -e 's|https://download-r2.pytorch.org|https://mirrors.nju.edu.cn/pytorch|g' \
   -e 's|https://download.pytorch.org|https://mirrors.nju.edu.cn/pytorch|g' \
   uv.lock
@@ -63,8 +63,9 @@ RUN sed -i \
 ENV UV_DEFAULT_INDEX=https://pypi.tuna.tsinghua.edu.cn/simple
 
 RUN --mount=type=cache,target=/root/.cache/uv \
-    uv sync --frozen --no-dev && \
+    uv sync --frozen --no-dev --refresh-package numpy --refresh-package mediapipe && \
     .venv/bin/python -c "import alembic" && \
+    .venv/bin/python -c "import numpy; import numpy.lib._index_tricks_impl" && \
     .venv/bin/python -c "import mediapipe as mp; print('mediapipe', mp.__version__)"
 
 ENV PATH="/app/.venv/bin:$PATH"