feat: Implement Discord app UI and settings management

- Added MainUI class for displaying voice state, status icon, and buttons.
- Introduced MainUIHandler to manage UI interactions and bridge communication.
- Created SettingsUI for displaying QR code and configuration instructions.
- Implemented SettingsUIHandler to manage settings and web server interactions.
- Developed WebHandler for handling HTTP requests for settings configuration.
- Updated AppRegistry to initialize with the new Discord app descriptor.
- Enhanced InteractionHandler to support keyboard interactions across app switches.
- Updated UIHandler to manage app switching and rendering of app icons.
- Enabled QR code support in LVGL configuration.

main/ui/apps/registry.h

@@ -13,6 +13,12 @@ public:
     return registry;
   }
 
+  /**
+   * @brief Initialize the app registry with built-in apps
+   *
+   */
+  esp_err_t init(void);
+
   void register_app(std::unique_ptr<AppDescriptor> app_descriptor) {
     if (app_descriptors_.find(app_descriptor->get_name()) != app_descriptors_.end()) {
       // App already registered