Add build_clang/ to .gitignore

Ignoring Clang build directory to keep repository clean.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Peter Neiss

.gitignore

@@ -15,6 +15,7 @@ temp
 
 # CMake build directories
 build/
+build_clang/
 install_test/
 cmake-build-*/
 coverage_html/