feat: Add SDL3CPlusPlus game engine to gameengine/

Import SDL3CPlusPlus C++ game engine with:
- SDL3 + bgfx rendering backend
- Vulkan/Metal/DirectX shader support
- MaterialX material system
- Scene framework with ECS architecture
- Comprehensive test suite (TDD approach)
- Conan package management
- CMake build system

This provides the native C++ foundation for the Universal Platform's
Game and 3D capability modules.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

gameengine/debug_shader.cpp

@@ -0,0 +1,39 @@
+#include <iostream>
+#include <fstream>
+#include "src/services/impl/materialx_shader_generator.hpp"
+
+int main() {
+    sdl3cpp::services::impl::MaterialXShaderGenerator generator(nullptr);
+    
+    sdl3cpp::services::impl::MaterialXConfig config;
+    config.enabled = true;
+    config.shaderKey = "materialx";
+    config.useConstantColor = true;
+    config.constantColor = {0.8f, 0.2f, 0.2f};
+    config.libraryPath = "MaterialX/libraries";
+    
+    try {
+        auto paths = generator.Generate(config, std::filesystem::path("./scripts"));
+        
+        std::cout << "===== VERTEX SHADER =====\n";
+        std::cout << paths.vertexSource << std::endl;
+        std::cout << "\n===== FRAGMENT SHADER =====\n";
+        std::cout << paths.fragmentSource << std::endl;
+        
+        // Save to files
+        std::ofstream vfile("debug_vertex.glsl");
+        vfile << paths.vertexSource;
+        vfile.close();
+        
+        std::ofstream ffile("debug_fragment.glsl");
+        ffile << paths.fragmentSource;
+        ffile.close();
+        
+        std::cout << "\nShaders saved to debug_vertex.glsl and debug_fragment.glsl\n";
+    } catch (const std::exception& e) {
+        std::cerr << "Error: " << e.what() << std::endl;
+        return 1;
+    }
+    
+    return 0;
+}