various improvements

stopped using private header folder (for ease of development - for now)
implemented basic gui service (WIP)
added sdkconfig.defaults to the repo
updated docs

main/src/hello_world/hello_world.c

@@ -1,37 +1,62 @@
 #include "hello_world.h"
 #include <core_defines.h>
-
+#include <record.h>
 #include <nb_lvgl.h>
+#include <nb_hardware.h>
+#include <applications/services/gui/gui.h>
 #include <esp_lvgl_port.h>
 #include <esp_log.h>
-#include <nb_hardware.h>
 
 static const char* TAG = "app_helloworld";
 
 static void prv_on_button_click(lv_event_t _Nonnull* event) {
     ESP_LOGI(TAG, "button clicked");
+    // Open Gui record
+    Gui* gui = furi_record_open(RECORD_GUI);
+
+    // Free this screen
+    screen_id_t screen_id = (screen_id_t)event->user_data;
+    gui_screen_free(gui, screen_id);
+
+    // Close Gui record
+    furi_record_close(RECORD_GUI);
+    gui = NULL;
 }
 
-static int32_t prv_on_create(void* param) {
-    UNUSED(param);
+static void prv_hello_world_lvgl(lv_obj_t* parent, screen_id_t screen_id) {
     lvgl_port_lock(0);
 
-    lv_obj_t* lv_parent = lv_scr_act();
-
-    lv_obj_t* label = lv_label_create(lv_parent);
+    lv_obj_t* label = lv_label_create(parent);
     lv_label_set_recolor(label, true);
     lv_obj_set_width(label, 200);
     lv_obj_set_style_text_align(label, LV_TEXT_ALIGN_CENTER, 0);
     lv_label_set_text(label, "Hello, world!");
     lv_obj_align(label, LV_ALIGN_CENTER, 0, -30);
 
-    lv_obj_t* btn = lv_btn_create(lv_parent);
+    lv_obj_t* btn = lv_btn_create(parent);
     label = lv_label_create(btn);
-    lv_label_set_text_static(label, "Button");
+    lv_label_set_text_static(label, "Exit");
     lv_obj_align(btn, LV_ALIGN_CENTER, 0, 30);
-    lv_obj_add_event_cb(btn, prv_on_button_click, LV_EVENT_CLICKED, NULL);
+    lv_obj_add_event_cb(btn, prv_on_button_click, LV_EVENT_CLICKED, (void*)screen_id);
 
     lvgl_port_unlock();
+
+    // TODO: on app exit, call gui_screen_destroy()
+}
+
+static int32_t prv_hello_world_main(void* param) {
+    UNUSED(param);
+
+    // Open Gui record
+    Gui* gui = furi_record_open(RECORD_GUI);
+
+    // Register an lvgl screen
+    gui_screen_create(gui, &prv_hello_world_lvgl);
+
+    // Close Gui record
+    furi_record_close(RECORD_GUI);
+    gui = NULL;
+
     return 0;
 }
 
@@ -39,7 +64,7 @@ const nb_app_t hello_world_app = {
     .id = "helloworld",
     .name = "Hello World",
     .type = USER,
-    .entry_point = &prv_on_create,
+    .entry_point = &prv_hello_world_main,
     .stack_size = 2048,
     .priority = 10
 };

main/src/main.c

@@ -7,7 +7,7 @@
 // Apps
 #include "hello_world/hello_world.h"
 
-void app_main(void) {
+__attribute__((unused)) void app_main(void) {
     static nb_config_t config = {
         .display_driver = &board_2432s024_create_display_driver,
         .touch_driver = &board_2432s024_create_touch_driver,