模拟器构建入口改VS版本自适应（新增build_sim，兼容VS2019/2022/2026）；文档同步并补SDL2 SDK下载步骤

simulator/build_sim.bat

@@ -0,0 +1,24 @@
+@echo off
+rem ============================================================
+rem  LVGL PC simulator one-shot build (VS2019/2022/2026 auto-detect, x64)
+rem  Usage (from repo root, any shell):
+rem    & "simulator\build_sim.bat"                  incremental build
+rem    & "simulator\build_sim.bat" -Clean           full rebuild
+rem    & "simulator\build_sim.bat" -Config Release  Release build
+rem  Logic lives in build_sim.ps1 (vswhere probe -> generator mapping);
+rem  this bat only bypasses the PowerShell execution policy and
+rem  forwards the arguments. Exit code = build result (0 ok / 1 fail / 3 env).
+rem  NOTE: keep this file PURE ASCII - cmd parses .bat in the ANSI
+rem  codepage; UTF-8 Chinese here corrupts the command lines.
+rem ============================================================
+setlocal
+
+where pwsh >nul 2>nul
+if %errorlevel%==0 (
+    pwsh -NoProfile -ExecutionPolicy Bypass -File "%~dp0build_sim.ps1" %*
+    goto :done
+)
+powershell -NoProfile -ExecutionPolicy Bypass -File "%~dp0build_sim.ps1" %*
+
+:done
+exit /b %errorlevel%