robots.txt policy: Allow everything, explicitly

Every crawler on this index is named and allowed. Use when you want maximum reach into search and assistants and have nothing to withhold. An empty robots.txt already allows everything, so this file is not about permission — it is about being explicit. Naming each token means a later change is a one-line diff instead of a rewrite, and it documents that the allow was a decision. This is the policy this site itself serves. curl -s https://www.pathwren.workers.dev/robots/allow-all.txt