Add ERPNext Dockerfile + build script for automated security rebuilds

- erpnext/Dockerfile: builds from frappe/erpnext:v15 base with custom apps
- erpnext/build.sh: stages custom apps into build context before docker build
- Container update script now runs build.sh pre-build + extracts assets post-build
- ERPNext will auto-rebuild nightly when base image has security patches

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

erpnext/build.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+# Pre-build step: copy custom Frappe apps into the erpnext/ build context.
+# Called automatically by the container update script before docker compose build.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_ROOT="$(dirname "$SCRIPT_DIR")"
+
+echo "Staging custom apps into $SCRIPT_DIR..."
+for app in frappe_crypto frappe_adyen frappe_ca_registry performancewest_erpnext; do
+    rm -rf "$SCRIPT_DIR/$app"
+    cp -a "$REPO_ROOT/$app" "$SCRIPT_DIR/$app"
+done
+echo "Done. Ready for docker compose build erpnext."