Add local dev setup, fix BRouter Dockerfile, archive change (#12)

scripts/download-dev-segments.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+set -euo pipefail
+
+# Download a minimal BRouter segment for local development.
+# E10_N50 covers the Berlin area (~124MB) — enough for route testing.
+
+VOLUME_NAME="trails-cool_brouter_segments"
+SEGMENT="E10_N50.rd5"
+URL="https://brouter.de/brouter/segments4/${SEGMENT}"
+
+# Check if segment already exists in the Docker volume
+if docker run --rm -v "${VOLUME_NAME}:/data" alpine test -f "/data/${SEGMENT}" 2>/dev/null; then
+  echo "✓ Segment ${SEGMENT} already exists, skipping download"
+  exit 0
+fi
+
+echo "Downloading ${SEGMENT} (~124MB) for local development..."
+docker run --rm -v "${VOLUME_NAME}:/data" alpine/curl \
+  -L -o "/data/${SEGMENT}" "${URL}"
+
+echo "✓ Segment downloaded to Docker volume ${VOLUME_NAME}"