Add spec.md to .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: TimDettmers

.gitignore

@@ -158,4 +158,5 @@ cuda_build
 output/
 cuda-spec.md
 cuda-spec-additions.md
+spec.md
 agents/*_issues.json