Build: Add out/ directory to .gitignore

Fix Claude Code performance warning:
- Repository snapshot was tracking 385+ untracked files in out/ directory
- out/ contains build artifacts (binaries, intermediate objects)
- Adding out/ to .gitignore resolves the warning

Impact: Improves Claude Code repository scanning performance

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

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

.gitignore

@@ -4,6 +4,7 @@
 *.a
 *.exe
 *.d
+out/
 bench_allocators
 bench_asan
 test_hakmem