Fix permission errors: make chai_lab dirs writable for K8s

K8s runs containers as non-root. Chai-1 tries to download model
weights to /opt/conda/.../downloads which fails with PermissionError.
Set writable dirs and env vars for matplotlib, HF, and chai downloads.

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

Dockerfile

@@ -4,7 +4,10 @@ FROM pytorch/pytorch:2.6.0-cuda12.4-cudnn9-runtime
 # Set environment variables
 ENV DEBIAN_FRONTEND=noninteractive \
     PYTHONUNBUFFERED=TRUE \
-    PYTHONFAULTHANDLER=1
+    PYTHONFAULTHANDLER=1 \
+    MPLCONFIGDIR=/tmp/matplotlib \
+    CHAI_DOWNLOADS_DIR=/tmp/chai_downloads \
+    HF_HOME=/tmp/hf_home
 
 # Set working directory
 WORKDIR /workspace
@@ -14,6 +17,13 @@ RUN pip install --no-cache-dir \
     chai_lab==0.5.2 \
     "transformers>=4.30.0,<5.0.0"
 
+# Make package dirs writable for any user (K8s may run as non-root)
+RUN chmod -R a+rw /opt/conda/lib/python3.11/site-packages/chai_lab/ && \
+    mkdir -p /opt/conda/lib/python3.11/site-packages/downloads && \
+    chmod -R a+rw /opt/conda/lib/python3.11/site-packages/downloads && \
+    mkdir -p /tmp/chai_downloads /tmp/hf_home /tmp/matplotlib && \
+    chmod -R 777 /tmp/chai_downloads /tmp/hf_home /tmp/matplotlib
+
 # Verify installations
 RUN python -c "import torch; print(f'PyTorch: {torch.__version__}')" && \
     python -c "import transformers; print(f'transformers: {transformers.__version__}')" && \