chore: gitignore .tool-versions (asdf)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.gitignore

@@ -108,3 +108,6 @@ sync_report*.txt
 
 # Hypatia scan cache (local-only)
 .hypatia/
+
+# asdf version manager
+.tool-versions