Checkpoint 2: integrate native Editor, MCP, gameplay builds and standalone export

include/faset/player/SceneView.hpp

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+#pragma once
+#include <faset/render/renderer.hpp>
+#include <filesystem>
+#include <memory>
+#include <nlohmann/json.hpp>
+
+namespace faset::player {
+struct CameraSettings {
+    // Defaults frame the small demo scenes. An explicit editor camera overrides
+    // scene camera components without changing the authoring document.
+    bool overrideSceneCamera{false};
+    render::Vec3 eye{8, 6, 10};
+    render::Vec3 target{0, 0, 0};
+    float verticalFovDegrees{60};
+    float orthographicHeight{12};
+    float nearPlane{0.1f}, farPlane{1000};
+};
+class SceneView {
+  public:
+    // cacheRoot contains assets/<AssetId>/current.json and generation folders.
+    explicit SceneView(std::filesystem::path cacheRoot);
+    ~SceneView();
+    SceneView(const SceneView&) = delete;
+    SceneView& operator=(const SceneView&) = delete;
+    render::Snapshot build(const nlohmann::json& flatSceneOrRuntimeSnapshot, float aspect,
+                           CameraSettings camera = {});
+    void clearCache();
+    const std::vector<std::string>& diagnostics() const;
+
+  private:
+    struct Impl;
+    std::unique_ptr<Impl> impl_;
+};
+
+// Reads JSON development scenes or a strict FASETSCN v1 CBOR envelope.
+nlohmann::json readScene(const std::filesystem::path& path);
+} // namespace faset::player