Add full app source

Adds the Flutter inventory app source, cleaned up for a shared repo:
generic package name, no hardcoded ERP endpoints (moved to gitignored
local config), no dead auth code, no debug logging of session data.

lib/controllers/simple_ui_controller.dart

@@ -0,0 +1,9 @@
+import 'package:get/get.dart';
+
+class SimpleUIController extends GetxController {
+  RxBool isObscure = true.obs;
+
+  isObscureActive() {
+    isObscure.value = !isObscure.value;
+  }
+}