fix: add libexpat1 to runtime Docker image — fixes STAC indicator data

pystac-client depends on libexpat.so.1 which was installed in the
builder stage but not in the runtime stage. All STAC-based indicators
(cropland, vegetation, water) were silently falling back to placeholder
data because of this missing library.

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Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

Dockerfile

@@ -34,6 +34,7 @@ FROM python:3.11-slim
 RUN apt-get update && apt-get install -y --no-install-recommends \
     libgeos-c1v5 \
     libproj25 \
+    libexpat1 \
     proj-data \
     proj-bin \
     && rm -rf /var/lib/apt/lists/*