feat(shaders_lab): uniform annotations → auto-generated ImGui controls

- cpp/functions/gfx/uniform_parser: regex-based parser of @slider/@color/@toggle/@xy annotations (+ inline tests)
- cpp/functions/gfx/uniform_panel: ImGui widgets + value store + glUniform* apply
- shader_canvas: optional uniforms callback invoked per-frame
- gl_loader: +glUniform1i/3f/4f
- seed plasma: demo uniforms u_speed + u_color
- rebuild Windows .exe

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

cpp/functions/gfx/shader_canvas.h

@@ -1,4 +1,5 @@
 #pragma once
+#include <functional>
 #include <string>
 #include "gfx/gl_framebuffer.h"
 #include "gfx/gl_shader.h"
@@ -21,7 +22,9 @@ void canvas_set_program(ShaderCanvas& c, unsigned int program);
 
 // Renderiza el shader al FBO y dibuja la textura resultante como contenido del panel ImGui.
 // Llamar DENTRO de un ImGui::Begin/End. Ocupa GetContentRegionAvail().
-void canvas_render(ShaderCanvas& c, float time_seconds);
+// uniforms_fn se invoca tras glUseProgram y antes de quad_draw, recibe el program ID.
+void canvas_render(ShaderCanvas& c, float time_seconds,
+                   const std::function<void(unsigned int program)>& uniforms_fn = {});
 
 void canvas_destroy(ShaderCanvas& c);