Add one-shot server installer (curl | sh)

server/install.sh bootstraps deploy.sh + mods.json into a temp dir so the
server can be installed with a single piped command.

server/install.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+#
+# Reaper's Sky - one-shot server installer.
+#
+# Fetches deploy.sh + mods.json from the repo into a temp dir, then runs
+# deploy.sh with bash. Keeps it runnable via a single pipe:
+#
+#   curl -sSL <this-raw-url> | sh
+#
+# Needs: curl, bash, python3 (apt-installed by deploy.sh on Debian 13).
+set -eu
+
+BASE="https://git.reaperofveriod.nl/ReaperOfVeriod/Reaper-s-Sky/raw/branch/main/server"
+TMP="$(mktemp -d)"
+
+cleanup() { rm -rf "$TMP"; }
+trap cleanup EXIT INT TERM
+
+cd "$TMP"
+curl -fsSL -o deploy.sh "$BASE/deploy.sh"
+curl -fsSL -o mods.json "$BASE/mods.json"
+exec bash deploy.sh "$@"