Document design choices and standardize Dockerfile

scripts/build-linux-docker.sh

@@ -1,12 +1,21 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
+# Optional first argument mirrors build-linux.sh. The Docker build still writes
+# the final artifact into the local dist/ tree, not into the container.
 output="${1:-dist/linux/pysentry}"
 
-docker build -f Dockerfile.linux -t pysentry-linux-builder .
+# Dockerfile contains the native packages required by Fyne. Keeping that
+# environment in Docker makes Linux builds repeatable from Windows hosts and CI.
+docker build -f Dockerfile -t pysentry-linux-builder .
+
+# The image build produces /out/pysentry. A temporary container is used only as a
+# convenient way to copy that file out; the app is not run inside the container.
 container_id="$(docker create pysentry-linux-builder)"
 mkdir -p "$(dirname "$output")"
 docker cp "${container_id}:/out/pysentry" "$output"
 docker rm "$container_id" >/dev/null
 
+# Icons are embedded in the Go binary, so there is no assets directory to copy
+# after extracting the Linux executable.
 echo "Built $output"