Add Windows build scripts, fix multi-threaded MPQ extraction, and cross-platform temp paths

- Add build.ps1/bat, rebuild.ps1/bat, debug_texture.ps1/bat (Windows equivalents
  of existing bash scripts, using directory junctions for Data link)
- Fix asset extractor: StormLib is not thread-safe even with separate handles per
  thread. Serialize all MPQ reads behind a mutex while keeping CRC computation and
  disk writes parallel. Previously caused 99.8% extraction failures with >1 thread.
- Add SFileHasFile() check during enumeration to skip listfile-only entries
- Add diagnostic logging for extraction failures (first 5 per thread + summary)
- Use std::filesystem::temp_directory_path() instead of hardcoded /tmp/ in
  character_renderer.cpp debug dumps
- Update debug_texture.sh to use $TMPDIR fallback and glob for actual dump filenames

build.bat

@@ -0,0 +1,3 @@
+@echo off
+REM Convenience wrapper — launches the PowerShell build script.
+powershell -ExecutionPolicy Bypass -File "%~dp0build.ps1" %*