feat: add DemoApp and ShutdownApp classes for interactive UI components and shutdown management

main/ui/apps/demo_app.h

@@ -0,0 +1,53 @@
+#pragma once
+
+#include "ui/ui_app.h"
+#include "ui/app_registry.h"
+
+/**
+ * @brief Demo application - counter and brightness slider
+ *
+ * Demonstrates interactive UI components with touch input:
+ * - Counter display with increment/decrement buttons
+ * - Brightness slider
+ */
+class DemoApp : public UIApp {
+public:
+  DemoApp() = default;
+  virtual ~DemoApp() = default;
+
+  esp_err_t init(lv_obj_t* container) override;
+  esp_err_t deinit(void) override;
+  std::string get_name(void) const override;
+
+private:
+  // UI components
+  lv_obj_t* _label_header= nullptr;
+  lv_obj_t* _label_counter= nullptr;
+  lv_obj_t* _btn_increment= nullptr;
+  lv_obj_t* _btn_decrement= nullptr;
+  lv_obj_t* _slider_brightness= nullptr;
+  lv_obj_t* _label_slider_value= nullptr;
+
+  // State
+  int _counter= 0;
+
+  // Event callbacks
+  static void btn_increment_event_cb(lv_event_t* e);
+  static void btn_decrement_event_cb(lv_event_t* e);
+  static void slider_event_cb(lv_event_t* e);
+};
+
+/**
+ * @brief AppDescriptor for DemoApp
+ *
+ * Registers the demo app with the AppRegistry and provides
+ * icon rendering functionality.
+ */
+class DemoAppDescriptor : public AppDescriptor {
+public:
+  DemoAppDescriptor();
+  void draw_icon(lv_obj_t* parent) override;
+
+private:
+  static DemoApp* _app_instance;
+};