add windows build script

lightningbeam-ui/build-windows.bat

@@ -0,0 +1,29 @@
+@echo off
+REM Build script for Windows
+REM Requires: FFmpeg 8.0.0 dev files in C:\ffmpeg, LLVM installed
+
+REM FFmpeg location (headers + libs + DLLs)
+if not defined FFMPEG_DIR set FFMPEG_DIR=C:\ffmpeg
+
+REM LLVM/libclang for bindgen (ffmpeg-sys-next)
+if not defined LIBCLANG_PATH set LIBCLANG_PATH=C:\Program Files\LLVM\bin
+
+REM Validate prerequisites
+if not exist "%FFMPEG_DIR%\include\libavcodec\avcodec.h" (
+    echo ERROR: FFmpeg dev files not found at %FFMPEG_DIR%
+    echo Download FFmpeg 8.0.0 shared+dev from https://github.com/GyanD/codexffmpeg/releases
+    echo and extract to %FFMPEG_DIR%
+    exit /b 1
+)
+
+if not exist "%LIBCLANG_PATH%\libclang.dll" (
+    echo ERROR: LLVM/libclang not found at %LIBCLANG_PATH%
+    echo Install with: winget install LLVM.LLVM
+    exit /b 1
+)
+
+echo Building Lightningbeam Editor...
+echo   FFMPEG_DIR=%FFMPEG_DIR%
+echo   LIBCLANG_PATH=%LIBCLANG_PATH%
+
+cargo build --package lightningbeam-editor %*