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/theme_controller.dart

@@ -0,0 +1,29 @@
+import 'package:flutter/material.dart';
+import 'package:get/get.dart';
+import 'package:get_storage/get_storage.dart';
+
+class ThemeController extends GetxController {
+  final _box = GetStorage();
+  final _key = 'isDarkMode';
+
+  RxBool isDarkMode = false.obs;
+
+  @override
+  void onInit() {
+    super.onInit();
+    isDarkMode.value = _loadThemeFromBox();
+    Get.changeThemeMode(isDarkMode.value ? ThemeMode.dark : ThemeMode.light);
+  }
+
+  bool _loadThemeFromBox() => _box.read(_key) ?? false;
+
+  void _saveThemeToBox(bool value) => _box.write(_key, value);
+
+  ThemeMode get theme => isDarkMode.value ? ThemeMode.dark : ThemeMode.light;
+
+  void toggleTheme() {
+    isDarkMode.value = !isDarkMode.value;
+    _saveThemeToBox(isDarkMode.value);
+    Get.changeThemeMode(isDarkMode.value ? ThemeMode.dark : ThemeMode.light);
+  }
+}