feat(@projects/@magic-civilization): ✨ add headless gut test runner script

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

tools/gut-headless.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+# Runs the GUT headless test suite — mirrors the CI "headless GUT" step exactly.
+# Usage: bash tools/gut-headless.sh [extra gut flags]
+set -uo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+
+flatpak run --filesystem=home org.godotengine.Godot \
+  --path "$REPO_ROOT/src/game" \
+  --headless \
+  -s addons/gut/gut_cmdln.gd \
+  -gdir=engine/tests/unit \
+  -gexit \
+  "$@"