feat(travel): Implement settings UI and web server for MTR route configuration

- Added MainUIHandler class to manage the main UI and polling for arrival data.
- Introduced SettingsUI class for displaying QR code and configuration options.
- Created SettingsUIHandler to manage settings UI lifecycle and web server interactions.
- Developed WebHandler to handle HTTP requests for MTR route settings, including adding and removing routes.
- Implemented web endpoints for fetching MTR lines, routes, and saving settings.
- Enhanced UI with responsive design for e-ink displays and added error handling for web interactions.

main/ui/apps/travel/settings/settings_handler.h

@@ -0,0 +1,58 @@
+#pragma once
+
+#include "freertos/FreeRTOS.h"
+#include <string>
+#include <vector>
+#include <memory>
+#include "io/nvs_handler.h"
+#include "ui/apps/travel/types.h"
+
+namespace travel {
+
+/**
+ * @brief Settings handler for Travel app
+ *
+ * Manages NVS persistence of route pairs and polling interval.
+ */
+class SettingHandler {
+public:
+  explicit SettingHandler(std::unique_ptr<NVSStorageHandler> storage);
+  ~SettingHandler() = default;
+
+  esp_err_t init(const EventGroupHandle_t& system_event_group);
+
+  void load_settings();
+  void save_settings();
+
+  bool is_configured() const { return !routes_.empty(); }
+
+  // Route management
+  void add_route(const RoutePair& route);
+  void remove_route(size_t index);
+  void clear_routes();
+  const std::vector<RoutePair>& get_routes() const { return routes_; }
+  size_t get_route_count() const { return routes_.size(); }
+
+  // Polling interval (seconds)
+  uint32_t get_polling_interval() const { return polling_interval_sec_; }
+  void set_polling_interval(uint32_t seconds);
+
+  static constexpr size_t MAX_ROUTES = 5;
+  static constexpr uint32_t DEFAULT_POLLING_INTERVAL = 30;
+  static constexpr uint32_t MIN_POLLING_INTERVAL = 10;
+  static constexpr uint32_t MAX_POLLING_INTERVAL = 120;
+
+private:
+  static constexpr const char* NVS_KEY_ROUTES = "routes";
+  static constexpr const char* NVS_KEY_POLLING = "poll_interval";
+
+  std::vector<RoutePair> routes_;
+  uint32_t polling_interval_sec_ = DEFAULT_POLLING_INTERVAL;
+  std::unique_ptr<NVSStorageHandler> storage_;
+
+  // JSON serialization helpers
+  std::string routes_to_json() const;
+  void routes_from_json(const std::string& json);
+};
+
+} // namespace travel