feat: add MTR Next Train application with multi-page navigation and real-time arrival info

main/ui/apps/mtr_app.h

@@ -0,0 +1,71 @@
+#pragma once
+
+#include "ui/ui_app.h"
+#include "ui/app_registry.h"
+#include "ui/page_stack.h"
+#include "external/mtr/mtr.h"
+#include "external/mtr/line_info.h"
+#include "external/mtr/station_info.h"
+#include "network/network.h"
+#include <memory>
+#include <string>
+
+/**
+ * @brief MTR Next Train application
+ *
+ * Provides multi-page navigation for:
+ * 1. Line selection - choose MTR line
+ * 2. Station selection - choose station within selected line
+ * 3. Arrival display - show real-time train arrival information
+ */
+class MtrApp : public UIApp {
+public:
+  MtrApp();
+  virtual ~MtrApp() = default;
+
+  esp_err_t init(lv_obj_t* container) override;
+  esp_err_t deinit(void) override;
+  std::string get_name(void) const override;
+  bool on_back_button_pressed(void) override;
+  void handle_event(uint32_t event_type, void* event_data) override;
+
+  // Set network handler (must be called before using app)
+  void set_network_handler(NetworkHandler* handler) { _network_handler = handler; }
+
+private:
+  std::unique_ptr<MTRNextTrainHandler> _mtr_handler;
+  std::unique_ptr<PageStack> _page_stack;
+  NetworkHandler* _network_handler = nullptr;
+
+  // Current selection state
+  std::string _selected_line_code;
+  std::string _selected_station_code;
+  LineInfo* _selected_line_info = nullptr;
+  std::vector<LineInfo> _all_lines;
+
+  // Page builders
+  void build_line_selection_page(lv_obj_t* page_container);
+  void build_station_selection_page(lv_obj_t* page_container);
+  void build_arrival_page(lv_obj_t* page_container);
+
+  // Event handlers
+  static void line_button_event_cb(lv_event_t* e);
+  static void station_button_event_cb(lv_event_t* e);
+  static void refresh_button_event_cb(lv_event_t* e);
+
+  // Helper functions
+  void load_arrival_data(lv_obj_t* page_container);
+  uint32_t parse_color_hex(const char* hex_str);
+};
+
+/**
+ * @brief AppDescriptor for MtrApp
+ */
+class MtrAppDescriptor : public AppDescriptor {
+public:
+  MtrAppDescriptor();
+  void draw_icon(lv_obj_t* parent) override;
+
+private:
+  static MtrApp* _app_instance;
+};