refactor: make ARNES external-repo based with ticket publish flow

scripts/install_into_repo.sh

@@ -0,0 +1,66 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SRC_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+TARGET_INPUT="${1:-}"
+
+if [ -z "$TARGET_INPUT" ]; then
+  echo "Usage: ./scripts/install_into_repo.sh /path/to/target-repo"
+  exit 1
+fi
+
+mkdir -p "$TARGET_INPUT"
+TARGET_ROOT="$(cd "$TARGET_INPUT" && pwd)"
+
+if [ "$TARGET_ROOT" = "$SRC_ROOT" ]; then
+  echo "Refusing to install ARNES into its own source repository. Use a different project repo."
+  exit 1
+fi
+
+if ! git -C "$TARGET_ROOT" rev-parse --is-inside-work-tree >/dev/null 2>&1; then
+  echo "No git repo detected at target. Initializing git repository..."
+  git -C "$TARGET_ROOT" init >/dev/null
+fi
+
+copy_item() {
+  local item="$1"
+  if [ -d "$SRC_ROOT/$item" ]; then
+    mkdir -p "$TARGET_ROOT/$item"
+    cp -R "$SRC_ROOT/$item"/. "$TARGET_ROOT/$item"/
+  else
+    cp "$SRC_ROOT/$item" "$TARGET_ROOT/$item"
+  fi
+}
+
+ITEMS=(
+  AGENTS.md
+  AGENTS.local.md.example
+  CHECKPOINTS.md
+  HOWTO.md
+  HOWTO-FEATURE.md
+  README.md
+  TEMPLATE.md
+  Makefile
+  requirements.txt
+  backlog
+  defaults
+  docs
+  features
+  harness
+  platforms
+  project
+  scripts
+  spec
+  starter-pack
+  work
+)
+
+for item in "${ITEMS[@]}"; do
+  copy_item "$item"
+done
+
+echo "Installed ARNES core into: $TARGET_ROOT"
+echo "Next steps:"
+echo "  cd $TARGET_ROOT"
+echo "  ./scripts/start.sh"
+echo "  ./scripts/verify.sh"