refactor: fase 2 — elimina malloc/free a jdraw8 i paletes d'escenes

- JD8_Init/Quit: new[]/delete[] per a screen, main_palette, pixel_data
- JD8_NewSurface/FreeSurface: new Uint8[64000]{}/delete[]
- JD8_LoadPalette: uniforme — sempre retorna `new Color[256]`, copiant del
  LoadPalette extern al path no-cached (l'intermedi raw es frees amb free()
  perquè gif.h el malloca)
- JD8_SetScreenPalette: delete[] la paleta reemplaçada
- slides/secreta/menu/banner/mort scenes: std::free/std::malloc → delete[]/new Color[256]

Ownership uniforme: tot el cicle de vida de surface/palette usa new[]/delete[].

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

source/scenes/mort_scene.cpp

@@ -22,7 +22,7 @@ namespace scenes {
         // la paleta temporal immediatament.
         JD8_Palette pal = JD8_LoadPalette("gfx/gameover.gif");
         fade_.startFadeTo(pal);
-        std::free(pal);
+        delete[] pal;
 
         phase_ = Phase::FadingIn;
         remaining_ms_ = 10000;