feat: Enhance ScriptEngine with Shader and Scene Management

- Added ShaderManager to handle shader paths loading from Lua.
- Integrated SceneManager for managing scene objects within ScriptEngine.
- Updated ScriptEngine to utilize ShaderManager and SceneManager.
- Refactored audio command handling to use AudioManager.
- Improved error handling and Lua integration for shader and scene loading.
- Cleaned up code structure and dependencies in script_engine.hpp.

src/script/shader_manager.cpp

@@ -0,0 +1,74 @@
+#include "script/shader_manager.hpp"
+
+#include <lua.hpp>
+
+#include <stdexcept>
+#include <string>
+#include <unordered_map>
+
+namespace sdl3cpp::script {
+
+ShaderManager::ShaderManager(lua_State* L) : L_(L) {}
+
+std::unordered_map<std::string, ShaderManager::ShaderPaths> ShaderManager::LoadShaderPathsMap() {
+    lua_getglobal(L_, "get_shader_paths");
+    if (!lua_isfunction(L_, -1)) {
+        lua_pop(L_, 1);
+        throw std::runtime_error("Lua function 'get_shader_paths' is missing");
+    }
+    if (lua_pcall(L_, 0, 1, 0) != LUA_OK) {
+        std::string message = GetLuaError();
+        lua_pop(L_, 1);
+        throw std::runtime_error("Lua get_shader_paths failed: " + message);
+    }
+    if (!lua_istable(L_, -1)) {
+        lua_pop(L_, 1);
+        throw std::runtime_error("'get_shader_paths' did not return a table");
+    }
+
+    std::unordered_map<std::string, ShaderPaths> shaderMap;
+    lua_pushnil(L_);
+    while (lua_next(L_, -2) != 0) {
+        if (lua_isstring(L_, -2) && lua_istable(L_, -1)) {
+            std::string key = lua_tostring(L_, -2);
+            shaderMap.emplace(key, ReadShaderPathsTable(-1));
+        }
+        lua_pop(L_, 1);
+    }
+
+    lua_pop(L_, 1);
+    if (shaderMap.empty()) {
+        throw std::runtime_error("'get_shader_paths' did not return any shader variants");
+    }
+    return shaderMap;
+}
+
+ShaderManager::ShaderPaths ShaderManager::ReadShaderPathsTable(int index) {
+    ShaderPaths paths;
+    int absIndex = lua_absindex(L_, index);
+
+    lua_getfield(L_, absIndex, "vertex");
+    if (!lua_isstring(L_, -1)) {
+        lua_pop(L_, 1);
+        throw std::runtime_error("Shader path 'vertex' must be a string");
+    }
+    paths.vertex = lua_tostring(L_, -1);
+    lua_pop(L_, 1);
+
+    lua_getfield(L_, absIndex, "fragment");
+    if (!lua_isstring(L_, -1)) {
+        lua_pop(L_, 1);
+        throw std::runtime_error("Shader path 'fragment' must be a string");
+    }
+    paths.fragment = lua_tostring(L_, -1);
+    lua_pop(L_, 1);
+
+    return paths;
+}
+
+std::string ShaderManager::GetLuaError() {
+    const char* message = lua_tostring(L_, -1);
+    return message ? message : "unknown lua error";
+}
+
+} // namespace sdl3cpp::script