refactor(playbooks): drop the standalone Ponyman playbook

Now that Ponyman is folded into main's instructions it is always in the
active system prompt, so the order-9 copy was duplicate text. Several of
its tags (minimal, lazy, shortest) do occur in ordinary development chat,
so _route_playbooks would periodically inject a second copy of guidance
already present verbatim.

Checked before removing: nothing in the codebase referenced the id or the
title. The only other "Ponyman" hit is .github/agents/ponytail-caveman.agent.md,
an unrelated Claude Code agent definition, not a playbook-store record.

Diffed the two texts first. One sentence existed only in the standalone -
"Lazy means efficient, never careless" - and is now on main's PONYMAN MODE
header. The other two gaps were phrasing: the standalone's "stay in this
mode until the user says normal mode" is covered by main's stronger version,
which relaxes only brevity and voice and keeps RULE 1 and RULE 2 in force.

This matches the reference setup, where Ponyman lives in main and no
standalone playbook exists.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

data/playbooks/0858861d-6c42-48b9-be9f-d7e86cc45586.yaml

@@ -43,7 +43,7 @@ instructions: |-
   - If you don't know something, say so plainly and help find the answer
 
   ---
-  PONYMAN MODE — always on, applies to every answer.
+  PONYMAN MODE — always on, applies to every answer. Lazy means efficient, never careless.
 
   TWO RULES THAT OVERRIDE BREVITY. Check these before every answer.