添加 LightGame 关卡编辑器并修复死亡扣命、光感门阈值与渲染问题

- 新增 LevelEditor：ImGui 面板支持 tile 绘制、对象放置、选择、擦除、网格/碰撞体可视化、关卡导出为头文件
- 修复 LevelRenderer::draw 中 draw_tilemap 错误传入负 screen 坐标导致摄像机移动后 tile 消失
- 修复 Preview Light 滑块用 reinterpret_cast 将 uint16_t 强转为 int* 写入 4 字节覆盖相邻 bool 成员
- 修复编辑器放置光感门缺少 light_threshold 默认值导致不响应亮度变化
- 统一 LightPlatform[3192,4095] ShadowPlatform[0,1023] Door[1023,3192] 阈值到关卡数据与编辑器默认值
- 修复 SDL_StopTextInput 导致 ImGui InputText 无法输入及键盘状态异常
- 修复死亡状态每帧扣命导致一次死亡直接 GameOver
- 集成 ImGui (SDL2 Renderer 后端) 到构建系统

third_party/imgui/backends/imgui_impl_sdlrenderer2.h

@@ -0,0 +1,40 @@
+// dear imgui: Renderer Backend for SDL_Renderer for SDL2
+// (Requires: SDL 2.0.17+)
+
+// Note how SDL_Renderer is an _optional_ component of SDL2.
+// For a multi-platform app consider using e.g. SDL+DirectX on Windows and SDL+OpenGL on Linux/OSX.
+// If your application will want to render any non trivial amount of graphics other than UI,
+// please be aware that SDL_Renderer currently offers a limited graphic API to the end-user and
+// it might be difficult to step out of those boundaries.
+
+// Implemented features:
+//  [X] Renderer: User texture binding. Use 'SDL_Texture*' as ImTextureID. Read the FAQ about ImTextureID!
+//  [X] Renderer: Large meshes support (64k+ vertices) with 16-bit indices.
+
+// You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
+// Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
+// Learn about Dear ImGui:
+// - FAQ                  https://dearimgui.com/faq
+// - Getting Started      https://dearimgui.com/getting-started
+// - Documentation        https://dearimgui.com/docs (same as your local docs/ folder).
+// - Introduction, links and more at the top of imgui.cpp
+
+#pragma once
+#ifndef IMGUI_DISABLE
+#include "imgui.h"      // IMGUI_IMPL_API
+
+struct SDL_Renderer;
+
+// Follow "Getting Started" link and check examples/ folder to learn about using backends!
+IMGUI_IMPL_API bool     ImGui_ImplSDLRenderer2_Init(SDL_Renderer* renderer);
+IMGUI_IMPL_API void     ImGui_ImplSDLRenderer2_Shutdown();
+IMGUI_IMPL_API void     ImGui_ImplSDLRenderer2_NewFrame();
+IMGUI_IMPL_API void     ImGui_ImplSDLRenderer2_RenderDrawData(ImDrawData* draw_data, SDL_Renderer* renderer);
+
+// Called by Init/NewFrame/Shutdown
+IMGUI_IMPL_API bool     ImGui_ImplSDLRenderer2_CreateFontsTexture();
+IMGUI_IMPL_API void     ImGui_ImplSDLRenderer2_DestroyFontsTexture();
+IMGUI_IMPL_API bool     ImGui_ImplSDLRenderer2_CreateDeviceObjects();
+IMGUI_IMPL_API void     ImGui_ImplSDLRenderer2_DestroyDeviceObjects();
+
+#endif // #ifndef IMGUI_DISABLE