demo secrets and new build scripts

scripts/build.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Local build-only test script for Linux/macOS.
+# Compiles the project WITHOUT uploading to any device.
+# Useful to quickly check "does it even compile" without touching the M5Stack.
+#
+# Usage:
+#   ./scripts/build.sh
+
+cd "$(dirname "$0")/.."
+
+VENV_DIR=".venv-platformio"
+
+if [ ! -d "$VENV_DIR" ]; then
+    echo "Creating local virtualenv in $VENV_DIR ..."
+    python3 -m venv "$VENV_DIR"
+    "$VENV_DIR/bin/pip" install --upgrade pip
+    "$VENV_DIR/bin/pip" install platformio
+fi
+
+echo "Running build (no upload) ..."
+"$VENV_DIR/bin/pio" run
+
+echo "Build finished successfully."