feat(shaders_lab): add gl_loader + Windows cross-compile

- cpp/functions/gfx/gl_loader.{h,cpp,md}: mini loader para OpenGL 2.0+
  (Linux no-op via GL_GLEXT_PROTOTYPES, Windows wglGetProcAddress)
- Portar gl_shader/gl_framebuffer/fullscreen_quad/shader_canvas al loader
- CMakeLists: WIN32_EXECUTABLE para lanzar sin consola en Windows
- apps/shaders_lab/shaders_lab.exe: binario PE32+ precompilado

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

cpp/functions/gfx/gl_loader.cpp

@@ -0,0 +1,78 @@
+#include "gl_loader.h"
+
+#ifdef _WIN32
+
+PFNGLATTACHSHADERPROC        fn_glAttachShader        = nullptr;
+PFNGLBINDBUFFERPROC          fn_glBindBuffer          = nullptr;
+PFNGLBINDFRAMEBUFFERPROC     fn_glBindFramebuffer     = nullptr;
+PFNGLBINDVERTEXARRAYPROC     fn_glBindVertexArray     = nullptr;
+PFNGLCOMPILESHADERPROC       fn_glCompileShader       = nullptr;
+PFNGLCREATEPROGRAMPROC       fn_glCreateProgram       = nullptr;
+PFNGLCREATESHADERPROC        fn_glCreateShader        = nullptr;
+PFNGLDELETEBUFFERSPROC       fn_glDeleteBuffers       = nullptr;
+PFNGLDELETEFRAMEBUFFERSPROC  fn_glDeleteFramebuffers  = nullptr;
+PFNGLDELETEPROGRAMPROC       fn_glDeleteProgram       = nullptr;
+PFNGLDELETESHADERPROC        fn_glDeleteShader        = nullptr;
+PFNGLDELETEVERTEXARRAYSPROC  fn_glDeleteVertexArrays  = nullptr;
+PFNGLFRAMEBUFFERTEXTURE2DPROC fn_glFramebufferTexture2D = nullptr;
+PFNGLGENBUFFERSPROC          fn_glGenBuffers          = nullptr;
+PFNGLGENFRAMEBUFFERSPROC     fn_glGenFramebuffers     = nullptr;
+PFNGLGENVERTEXARRAYSPROC     fn_glGenVertexArrays     = nullptr;
+PFNGLGETPROGRAMINFOLOGPROC   fn_glGetProgramInfoLog   = nullptr;
+PFNGLGETPROGRAMIVPROC        fn_glGetProgramiv        = nullptr;
+PFNGLGETSHADERINFOLOGPROC    fn_glGetShaderInfoLog    = nullptr;
+PFNGLGETSHADERIVPROC         fn_glGetShaderiv         = nullptr;
+PFNGLGETUNIFORMLOCATIONPROC  fn_glGetUniformLocation  = nullptr;
+PFNGLLINKPROGRAMPROC         fn_glLinkProgram         = nullptr;
+PFNGLSHADERSOURCEPROC        fn_glShaderSource        = nullptr;
+PFNGLUNIFORM1FPROC           fn_glUniform1f           = nullptr;
+PFNGLUNIFORM2FPROC           fn_glUniform2f           = nullptr;
+PFNGLUSEPROGRAMPROC          fn_glUseProgram          = nullptr;
+
+namespace fn::gfx {
+
+bool gl_loader_init() {
+    #define LOAD(name) \
+        fn_##name = (decltype(fn_##name))wglGetProcAddress(#name); \
+        if (!fn_##name) return false
+
+    LOAD(glAttachShader);
+    LOAD(glBindBuffer);
+    LOAD(glBindFramebuffer);
+    LOAD(glBindVertexArray);
+    LOAD(glCompileShader);
+    LOAD(glCreateProgram);
+    LOAD(glCreateShader);
+    LOAD(glDeleteBuffers);
+    LOAD(glDeleteFramebuffers);
+    LOAD(glDeleteProgram);
+    LOAD(glDeleteShader);
+    LOAD(glDeleteVertexArrays);
+    LOAD(glFramebufferTexture2D);
+    LOAD(glGenBuffers);
+    LOAD(glGenFramebuffers);
+    LOAD(glGenVertexArrays);
+    LOAD(glGetProgramInfoLog);
+    LOAD(glGetProgramiv);
+    LOAD(glGetShaderInfoLog);
+    LOAD(glGetShaderiv);
+    LOAD(glGetUniformLocation);
+    LOAD(glLinkProgram);
+    LOAD(glShaderSource);
+    LOAD(glUniform1f);
+    LOAD(glUniform2f);
+    LOAD(glUseProgram);
+
+    #undef LOAD
+    return true;
+}
+
+} // namespace fn::gfx
+
+#else
+
+namespace fn::gfx {
+bool gl_loader_init() { return true; }
+} // namespace fn::gfx
+
+#endif