feat(engine): PostFX cycle + fixes de reinicialització i overflow

- Afegir handlePostFXCycle() amb 5 presets (vinyeta/scanlines/cromàtica/complet/off)
  i tecla X per ciclar-los (input_handler + engine.hpp)
- Augmentar MAX_SPRITES de 65536 a 200000 i afegir guard d'overflow a pushQuad()
- Netejar textures/objectes UI abans de reinicialitzar (AppLogo::initialize,
  UIManager::initialize) per evitar leaks en toggleRealFullscreen

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

source/engine.hpp

@@ -75,6 +75,9 @@ class Engine {
         void toggleRealFullscreen();
         void toggleIntegerScaling();
 
+        // PostFX presets
+        void handlePostFXCycle();
+
         // Modo kiosko
         void setKioskMode(bool enabled) { kiosk_mode_ = enabled; }
         bool isKioskMode() const { return kiosk_mode_; }
@@ -165,6 +168,7 @@ class Engine {
 
         // PostFX uniforms (passed to GPU each frame)
         PostFXUniforms postfx_uniforms_ = {1.5f, 0.0f, 0.0f, 0.0f};
+        int postfx_effect_mode_ = 0;
 
         // Sistema de zoom dinámico
         int current_window_zoom_ = DEFAULT_WINDOW_ZOOM;

source/gpu/gpu_sprite_batch.cpp

@@ -179,6 +179,7 @@ void GpuSpriteBatch::toNDC(float px, float py,
 void GpuSpriteBatch::pushQuad(float ndx0, float ndy0, float ndx1, float ndy1,
                                float u0, float v0, float u1, float v1,
                                float r, float g, float b, float a) {
+    if (vertices_.size() + 4 > static_cast<size_t>(MAX_SPRITES) * 4) return;
     uint32_t vi = static_cast<uint32_t>(vertices_.size());
 
     // TL, TR, BR, BL

source/gpu/gpu_sprite_batch.hpp

@@ -27,7 +27,7 @@ struct GpuVertex {
 class GpuSpriteBatch {
 public:
     // Maximum sprites (background + UI overlay each count as one sprite)
-    static constexpr int MAX_SPRITES = 65536;
+    static constexpr int MAX_SPRITES = 200000;
 
     bool init(SDL_GPUDevice* device);
     void destroy(SDL_GPUDevice* device);

source/input/input_handler.cpp

@@ -280,6 +280,11 @@ bool InputHandler::processEvents(Engine& engine) {
                     engine.toggleLogoMode();
                     break;
 
+                // Ciclar presets PostFX (vinyeta/scanlines/cromàtica/complet/desactivat)
+                case SDLK_X:
+                    engine.handlePostFXCycle();
+                    break;
+
                 // Toggle Debug Display (movido de H a F12)
                 case SDLK_F12:
                     engine.toggleDebug();

source/ui/app_logo.cpp

@@ -36,6 +36,11 @@ AppLogo::~AppLogo() {
 // ============================================================================
 
 bool AppLogo::initialize(SDL_Renderer* renderer, int screen_width, int screen_height) {
+    if (logo1_base_texture_)   { SDL_DestroyTexture(logo1_base_texture_);   logo1_base_texture_   = nullptr; }
+    if (logo1_native_texture_) { SDL_DestroyTexture(logo1_native_texture_); logo1_native_texture_ = nullptr; }
+    if (logo2_base_texture_)   { SDL_DestroyTexture(logo2_base_texture_);   logo2_base_texture_   = nullptr; }
+    if (logo2_native_texture_) { SDL_DestroyTexture(logo2_native_texture_); logo2_native_texture_ = nullptr; }
+
     renderer_ = renderer;
     base_screen_width_ = screen_width;
     base_screen_height_ = screen_height;

source/ui/ui_manager.cpp

@@ -70,6 +70,11 @@ UIManager::~UIManager() {
 void UIManager::initialize(SDL_Renderer* renderer, ThemeManager* theme_manager,
                           int physical_width, int physical_height,
                           int logical_width, int logical_height) {
+    delete text_renderer_debug_;    text_renderer_debug_    = nullptr;
+    delete text_renderer_notifier_; text_renderer_notifier_ = nullptr;
+    delete notifier_;               notifier_               = nullptr;
+    delete help_overlay_;           help_overlay_           = nullptr;
+
     renderer_ = renderer;
     theme_manager_ = theme_manager;
     physical_window_width_ = physical_width;