feat(world-sketcher): 新增本地服务器、标签显示和README重写

- 新增 server.py + start.bat: 本地保存/加载服务器
- sketch.html: 切换层级时自动绘制元素标签
- L1 显示区域名称+地形标高，L2 显示建筑名称+高度
- 保存优先POST到服务器，加载优先从output/读取
- 命名弹窗区分'地形标高'和'建筑高度'
- README 全面重写：双模式启动、文件结构、API端点、高度语义

tools/world-sketcher/start.bat

@@ -0,0 +1,23 @@
+@echo off
+title World Sketcher
+
+where python >nul 2>&1
+if %errorlevel% neq 0 (
+    echo [ERROR] Python not found. Install Python 3 first.
+    pause
+    exit /b 1
+)
+
+set PORT=8765
+if not "%~1"=="" set PORT=%~1
+
+echo.
+echo   World Sketcher
+echo   Port: %PORT%
+echo   Save dir: output\
+echo   Close this window to stop.
+echo.
+
+start "" cmd /c "timeout /t 2 /nobreak >nul & start http://localhost:%PORT%/sketch.html"
+
+python "%~dp0server.py" %PORT%