refactor: fase 5 — singletons a std::unique_ptr (elimina new/delete manual)

5 singletons afectats: Audio, Screen, Director, Resource::Cache, Resource::List.

- static T* instance → static std::unique_ptr<T> instance
- init(): new T() adoptat immediatament per unique_ptr (ownership RAII)
- destroy(): instance.reset() (sense delete manual)
- get(): retorna instance.get()
- Destructors moguts a public perquè std::default_delete hi pugui accedir
  (ctors privats + copy/move deleted → encapsulació efectiva mantinguda)

Ordre de destrucció preservat: SDL_AppQuit segueix cridant destroy() en
l'ordre invers a init() — la RAII automàtica no s'activa fins al final
del programa (LIFO de variables static).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

source/core/rendering/screen.cpp

@@ -55,19 +55,18 @@ namespace {
 }  // namespace
 #endif  // __EMSCRIPTEN__
 
-Screen* Screen::instance_ = nullptr;
+std::unique_ptr<Screen> Screen::instance_;
 
 void Screen::init() {
-    instance_ = new Screen();
+    instance_ = std::unique_ptr<Screen>(new Screen());
 }
 
 void Screen::destroy() {
-    delete instance_;
-    instance_ = nullptr;
+    instance_.reset();
 }
 
 auto Screen::get() -> Screen* {
-    return instance_;
+    return instance_.get();
 }
 
 Screen::Screen() {

source/core/rendering/screen.hpp

@@ -13,6 +13,8 @@ class Screen {
     static void destroy();
     static auto get() -> Screen*;
 
+    ~Screen();  // públic per a std::unique_ptr
+
     // Presentació — rep el buffer ARGB de 320x200 de JD8
     void present(Uint32* pixel_data);
 
@@ -62,7 +64,6 @@ class Screen {
 
    private:
     Screen();
-    ~Screen();
 
     void adjustWindowSize();
     void calculateMaxZoom();
@@ -70,7 +71,7 @@ class Screen {
     void applyFallbackPresentation();      // Logical presentation + scale mode per al path SDL_Renderer
     void ensureFallbackInternalTexture();  // Recrea internal_texture_sdl_ si cal (fallback path)
 
-    static Screen* instance_;
+    static std::unique_ptr<Screen> instance_;
 
     SDL_Window* window_{nullptr};
     SDL_Renderer* renderer_{nullptr};