feat: bundle 50m Natural Earth shapefiles in Docker for offline basemaps

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

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

Dockerfile

@@ -16,6 +16,12 @@ RUN pip install --no-cache-dir --only-binary :all: \
     numpy scipy matplotlib geopandas shapely pyproj rioxarray xarray \
     && pip install --no-cache-dir --prefer-binary cartopy
 
+# Pre-download 50m Natural Earth data so Cartopy works offline in containers
+RUN python -c "\
+import cartopy.io.shapereader as shpreader; \
+[shpreader.natural_earth(resolution='50m', category=cat, name=name) \
+ for cat, name in [('physical','land'),('physical','ocean'),('physical','coastline'),('cultural','admin_0_boundary_lines_lake')]]"
+
 # Install remaining deps (lightweight, pure-python or small wheels)
 RUN pip install --no-cache-dir --prefer-binary \
     "fastapi>=0.110.0" \
@@ -43,6 +49,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 # Copy installed packages from builder
 COPY --from=builder /usr/local/lib/python3.11/site-packages /usr/local/lib/python3.11/site-packages
 COPY --from=builder /usr/local/bin /usr/local/bin
+COPY --from=builder /root/.local/share/cartopy /root/.local/share/cartopy
 
 WORKDIR /app