refactor(build): enhance build_cleaner.py with .gitignore support and auto-discovery

- Added support for .gitignore patterns to the build_cleaner script, allowing it to respect ignored files during maintenance tasks.
- Implemented auto-discovery of CMake libraries marked for auto-maintenance, improving the automation of source list updates.
- Introduced functions for extracting includes and symbols from source files to suggest missing headers based on usage.
- Updated README to reflect new features and usage instructions.

Benefits:
- Streamlines the build process by automating maintenance tasks and ensuring proper header management.
- Enhances code organization and maintainability by integrating with existing project structures.

src/app/gui/core/background_renderer.cc

@@ -1,4 +1,4 @@
-#include "app/gui/app/background_renderer.h"
+#include "app/gui/core/background_renderer.h"
 
 #include <algorithm>
 #include <cmath>

src/app/gui/core/style.cc

@@ -4,7 +4,7 @@
 
 #include "util/file_util.h"
 #include "app/gui/core/theme_manager.h"
-#include "app/gui/app/background_renderer.h"
+#include "app/gui/core/background_renderer.h"
 #include "app/platform/font_loader.h"
 #include "app/gui/core/color.h"
 #include "app/gui/core/icons.h"

src/app/gui/gui_library.cmake

@@ -9,6 +9,7 @@
 
 # 1. Define Source Groups for each sub-library
 set(GUI_CORE_SRC
+  app/gui/core/background_renderer.cc
   app/gui/core/color.cc
   app/gui/core/input.cc
   app/gui/core/layout_helpers.cc
@@ -47,7 +48,6 @@ set(GUI_AUTOMATION_SRC
 
 set(GUI_APP_SRC
   app/gui/app/agent_chat_widget.cc
-  app/gui/app/background_renderer.cc
   app/gui/app/collaboration_panel.cc
   app/gui/app/editor_card_manager.cc
   app/gui/app/editor_layout.cc