Route UI state save through platform services

src/platform_windows/windows_platform_services.cpp

@@ -19,6 +19,7 @@ void win32_renderdoc_frame_start();
 void win32_renderdoc_frame_end();
 void win32_update_fps(int frames);
 void win32_update_stylus(float dt);
+void win32_save_window_state();
 
 namespace {
 
@@ -386,6 +387,11 @@ public:
         return { std::string(work_path) };
     }
 
+    void save_ui_state() override
+    {
+        win32_save_window_state();
+    }
+
     [[nodiscard]] bool enables_live_asset_reloading() override
     {
         return true;