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/ui_handler.h

@@ -53,13 +53,13 @@ public:
    * @brief Switch to a new app by its descriptor
    *
    * Deinitializes the current app (if any), initializes the new app,
-   * and updates the display. Holds shared ownership of the descriptor
-   * to ensure the app remains valid while active.
+   * and updates the display. The descriptor must remain valid in the
+   * AppRegistry for the lifetime of the app.
    *
-   * @param app_descriptor Shared pointer to the app descriptor
+   * @param app_descriptor Pointer to the app descriptor (managed by AppRegistry)
    * @return ESP_OK on success, error code otherwise
    */
-  esp_err_t switch_app(std::shared_ptr<AppDescriptor> app_descriptor);
+  esp_err_t switch_app(AppDescriptor* app_descriptor);
 
   /**
    * @brief Display shutdown screen
@@ -114,5 +114,5 @@ private:
 
   lv_obj_t* main_screen_ = nullptr;    ///< Root screen
   RootLayout root_layout_;            ///< Main screen layout manager
-  std::shared_ptr<AppDescriptor> active_descriptor_ = nullptr;  ///< Currently active app descriptor (shared ownership)
+  AppDescriptor* active_descriptor_ = nullptr;  ///< Currently active app descriptor (managed by AppRegistry)
 };