refactor(render): compose render frame orchestrator

Move the accepted draw transaction and failure recovery behind typed frame-phase owners so GameWindow only supplies immutable frame input. Preserve retail draw order, make ImGui/bootstrap shutdown ownership explicit, and restore exact text-render GL state on failures.\n\nCo-authored-by: Codex <codex@openai.com>

src/AcDream.UI.ImGui/ImGuiBootstrapper.cs

@@ -60,5 +60,15 @@ public sealed class ImGuiBootstrapper : IDisposable
     /// </summary>
     public void Render() => _controller.Render();
 
+    /// <summary>
+    /// Close an unfinished frame through the owning Silk controller. Silk's
+    /// controller clears its private frame-begun flag before uploading draw
+    /// data, so this is both the correct abort path for pre-render failures and
+    /// an idempotent no-op when a render upload failed after logical close.
+    /// Calling raw <c>ImGui.EndFrame</c> here would leave the controller's state
+    /// open and poison its next <see cref="BeginFrame"/> call.
+    /// </summary>
+    public void AbortFrame() => _controller.Render();
+
     public void Dispose() => _controller.Dispose();
 }