add demo app

scripts/pre-build-check.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+# Runs in the docker-cli container (Alpine, no Go toolchain — the actual
+# Go build happens inside the Dockerfile's golang:1.22-alpine builder
+# stage, not on the agent itself). Kept simple on purpose: this exists to
+# prove the hooks mechanism runs, not to be a real lint step.
+set -e
+echo "pre_build hook running for ${HOOK_REPO} (phase=${HOOK_PHASE})"
+test -f go.mod || { echo "go.mod missing"; exit 1; }
+test -f Dockerfile || { echo "Dockerfile missing"; exit 1; }
+echo "go.mod and Dockerfile both present — looks buildable."