fix: download Paper jar on CI runner and COPY into image

deploy/docker/download-paper.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+PAPER_VERSION="${PAPER_VERSION:-1.21}"
+PAPER_BUILD="${PAPER_BUILD:-latest}"
+OUT="${PAPER_OUT:-deploy/docker/downloads/paper.jar}"
+UA="rampart/1.0.0 (https://github.com/loki5512344/rampart)"
+
+mkdir -p "$(dirname "${OUT}")"
+
+if [ "${PAPER_BUILD}" = "latest" ]; then
+  PAPER_BUILD="$(curl -fsSL -H "User-Agent: ${UA}" \
+    "https://fill.papermc.io/v3/projects/paper/versions/${PAPER_VERSION}/builds" \
+    | jq -r 'first(.[] | select(.channel == "STABLE") | .id) // empty')"
+fi
+
+URL="$(curl -fsSL -H "User-Agent: ${UA}" \
+  "https://fill.papermc.io/v3/projects/paper/versions/${PAPER_VERSION}/builds" \
+  | jq -r --arg b "${PAPER_BUILD}" 'first(.[] | select(.id == ($b | tonumber)) | .downloads."server:default".url) // empty')"
+
+if [ -z "${URL}" ]; then
+  echo "error: no Paper download URL found for version ${PAPER_VERSION} build ${PAPER_BUILD}" >&2
+  exit 1
+fi
+
+echo "Downloading Paper ${PAPER_VERSION} build ${PAPER_BUILD}"
+case "${URL}" in
+  http*) JAR_URL="${URL}" ;;
+  *) JAR_URL="https://fill.papermc.io${URL}" ;;
+esac
+curl -fsSLo "${OUT}" -H "User-Agent: ${UA}" "${JAR_URL}"
+echo "Saved ${OUT}"