refactor(core/rendering): esborrar structs d'extensions GIF no usats (DEAD-09)

gif.hpp declarava Extension, GraphicControlExtension, ApplicationExtension
i PlaintextExtension com a tipus "empaquetats" per a llegir blocs del
stream GIF. El parser a gif.cpp, però, processa els bytes cru (avança
el punter i llig block_size + sub-blocs manualment) sense instanciar-los
mai. Les struct eren code pattern orientat a reus futurs que no va
arribar a materialitzar-se.

Build + smoke 5s xvfb OK (exit 124).

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

source/core/rendering/gif.hpp

@@ -42,28 +42,6 @@ namespace GIF {
         int len;
     };
 
-    struct Extension {
-        uint8_t extension_code;
-        uint8_t block_size;
-    };
-
-    struct GraphicControlExtension {
-        uint8_t fields;
-        uint16_t delay_time;
-        uint8_t transparent_color_index;
-    };
-
-    struct ApplicationExtension {
-        uint8_t application_id[8];
-        uint8_t version[3];
-    };
-
-    struct PlaintextExtension {
-        uint16_t left, top, width, height;
-        uint8_t cell_width, cell_height;
-        uint8_t foreground_color, background_color;
-    };
-
     class Gif {
        public:
         // Descompone (uncompress) el bloque comprimido usando LZW.