docs(entity_segment): reword the .claude/worktrees ignore rationale as a guard

The comment described worktrees living inside the project root as the current arrangement. They are kept outside the repository now, so the next reader cannot tell whether the rule is still live. Restate it as a guard against a worktree created inside the repository — the recursion it prevents is real and unchanged. The ignore pattern itself is untouched.

Closes #3612929