feat(gpu): afegir suport SPIRV (Vulkan) per Linux/Windows

- Nou: shaders/sprite.vert|frag, postfx.vert|frag, ball.vert (GLSL)
- Nou: cmake/spv_to_header.cmake — converteix .spv → uint8_t C header
- CMakeLists.txt: bloc non-Apple troba glslc, compila GLSL → SPIRV en
  build-time i genera headers embeguts a build/generated_shaders/
- gpu_context.cpp: MSL|METALLIB en Apple, SPIRV en la resta
- gpu_pipeline.cpp: createShaderSPIRV() + branques #ifdef __APPLE__
  per sprite/ball/postfx pipelines
- Corregeix crash a engine.cpp:821 (Windows/Linux) causat per pipelines
  null quan init() fallava en no trobar suport MSL

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

CMakeLists.txt

@@ -24,6 +24,48 @@ if (NOT SDL3_ttf_FOUND)
     message(FATAL_ERROR "SDL3_ttf no encontrado. Por favor, verifica su instalación.")
 endif()
 
+# ---- Shader compilation (non-Apple only: Vulkan/SPIRV) ----
+if(NOT APPLE)
+    find_program(GLSLC glslc HINTS "$ENV{VULKAN_SDK}/bin" "$ENV{VULKAN_SDK}/Bin")
+    if(NOT GLSLC)
+        message(FATAL_ERROR "glslc not found. Install the Vulkan SDK and ensure glslc is on PATH.")
+    endif()
+
+    set(SHADER_SRC_DIR "${CMAKE_SOURCE_DIR}/shaders")
+    set(SHADER_GEN_DIR "${CMAKE_BINARY_DIR}/generated_shaders")
+    file(MAKE_DIRECTORY "${SHADER_GEN_DIR}")
+
+    set(SPIRV_HEADERS)
+    foreach(SHADER sprite_vert sprite_frag postfx_vert postfx_frag ball_vert)
+        if(SHADER MATCHES "_vert$")
+            set(STAGE_FLAG "-fshader-stage=vertex")
+        else()
+            set(STAGE_FLAG "-fshader-stage=fragment")
+        endif()
+        string(REGEX REPLACE "_vert$" ".vert" GLSL_NAME "${SHADER}")
+        string(REGEX REPLACE "_frag$" ".frag" GLSL_NAME "${GLSL_NAME}")
+
+        set(GLSL_FILE "${SHADER_SRC_DIR}/${GLSL_NAME}")
+        set(SPV_FILE  "${SHADER_GEN_DIR}/${SHADER}.spv")
+        set(H_FILE    "${SHADER_GEN_DIR}/${SHADER}_spv.h")
+
+        add_custom_command(
+            OUTPUT "${H_FILE}"
+            COMMAND "${GLSLC}" ${STAGE_FLAG} -o "${SPV_FILE}" "${GLSL_FILE}"
+            COMMAND "${CMAKE_COMMAND}"
+                    -DINPUT="${SPV_FILE}"
+                    -DOUTPUT="${H_FILE}"
+                    -DVAR_NAME="k${SHADER}_spv"
+                    -P "${CMAKE_SOURCE_DIR}/cmake/spv_to_header.cmake"
+            DEPENDS "${GLSL_FILE}"
+            COMMENT "Compiling ${GLSL_NAME} to SPIRV"
+        )
+        list(APPEND SPIRV_HEADERS "${H_FILE}")
+    endforeach()
+
+    add_custom_target(shaders ALL DEPENDS ${SPIRV_HEADERS})
+endif()
+
 # Archivos fuente (excluir main_old.cpp)
 file(GLOB SOURCE_FILES source/*.cpp source/external/*.cpp source/boids_mgr/*.cpp source/gpu/*.cpp source/input/*.cpp source/scene/*.cpp source/shapes/*.cpp source/shapes_mgr/*.cpp source/state/*.cpp source/themes/*.cpp source/text/*.cpp source/ui/*.cpp)
 list(REMOVE_ITEM SOURCE_FILES "${CMAKE_SOURCE_DIR}/source/main_old.cpp")
@@ -60,6 +102,11 @@ set_target_properties(${PROJECT_NAME} PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAK
 # Enlazar las bibliotecas necesarias
 target_link_libraries(${PROJECT_NAME} ${LINK_LIBS})
 
+if(NOT APPLE)
+    add_dependencies(${PROJECT_NAME} shaders)
+    target_include_directories(${PROJECT_NAME} PRIVATE "${SHADER_GEN_DIR}")
+endif()
+
 # Tool: pack_resources
 add_executable(pack_resources tools/pack_resources.cpp source/resource_pack.cpp)
 target_include_directories(pack_resources PRIVATE ${CMAKE_SOURCE_DIR}/source)