refactor: fase 3 — Text::bitmap_ a std::vector<Uint8>

- bitmap_: Uint8* (owning, free'd al destructor) → std::vector<Uint8>
- loadBitmap copia des del buffer de LoadGif i fa free(pixels) de
  l'intermedi (gif.h usa malloc internament)
- ~Text() eliminat: regla 0 aplicada (vector es destrueix sol)
- Les 4 comprovacions !bitmap_ → bitmap_.empty()

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

source/core/rendering/text.hpp

@@ -5,11 +5,11 @@
 #include <cstdint>
 #include <string>
 #include <unordered_map>
+#include <vector>
 
 class Text {
    public:
     Text(const char* fnt_file, const char* gif_file);
-    ~Text();
 
     // Pinta texto sobre un buffer ARGB de 320x200
     void draw(Uint32* pixel_data, int x, int y, const char* text, Uint32 color) const;
@@ -46,7 +46,7 @@ class Text {
     int cell_spacing_{0};
     int row_spacing_{0};
 
-    Uint8* bitmap_{nullptr};  // píxels 8-bit del GIF de la font
+    std::vector<Uint8> bitmap_;  // píxels 8-bit del GIF de la font
     int bitmap_width_{0};
     int bitmap_height_{0};