Ignore claude worktree dirs in .gitignore

Per the new `.claude/wkts` subdir used in the `/open/close-wkt` skill we
just added.

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

Author: goodboy

.gitignore

@@ -136,3 +136,7 @@ gh/
 
 # LLM conversations that should remain private
 docs/conversations/
+
+# Claude worktrees
+.claude/wkts/
+claude_wkts