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/descriptor.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include "ui/apps/app.h"
+
+// Forward declaration
+class TravelApp;
+
+class TravelDescriptor : public AppDescriptor {
+public:
+  TravelDescriptor();
+  ~TravelDescriptor() override = default;
+
+  void draw_icon(lv_obj_t* parent) override;
+};