chore: gitignore .tool-versions (asdf)

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

Author: hyperpolymath

.gitignore

@@ -126,4 +126,6 @@ htmlcov/
 # Temp
 /tmp/
 *.tmp
-*.bak
+*.bak
+# asdf version manager
+.tool-versions