feat(skills): add /ponytail-gain measured-impact scoreboard (#108)

A one-shot scoreboard showing ponytail's measured benchmark impact
(less code, less cost, more speed) as plain ASCII bars, then points to
/ponytail-debt and /ponytail-audit for this repo's real numbers.

Complements the existing skills rather than duplicating them: debt
harvests the ponytail: ledger, audit finds what's cuttable, gain shows
the measured why-it-matters. No per-repo savings number is ever printed
-- the unbuilt version was never written, so there is no real baseline
to subtract from in a live repo. The bars carry the published benchmark
medians (5 tasks, 3 models); per-repo figures come from debt's count.

Ships every adapter the other commands ship: Claude commands/*.toml,
OpenCode .opencode/command/*.md, OpenClaw skill (generated), Pi command
registration. Help card, command enumeration, portability table, and
README updated in the same change.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

skills/ponytail-gain/SKILL.md

@@ -0,0 +1,50 @@
+---
+name: ponytail-gain
+description: >
+  Show ponytail's measured impact as a compact scoreboard: less code, less
+  cost, more speed, from the benchmark medians. One-shot display, not a
+  persistent mode, and not a per-repo number. Trigger: /ponytail-gain,
+  "ponytail gain", "what does ponytail save", "show ponytail impact",
+  "ponytail scoreboard".
+---
+
+# Ponytail Gain
+
+Display this scoreboard when invoked. One-shot: do NOT change mode, write flag
+files, or persist anything.
+
+The figures are the published benchmark medians (5 everyday tasks: email
+validator, debounce, CSV sum, countdown timer, rate limiter; three models:
+Haiku, Sonnet, Opus). They are measured, not computed from the current repo.
+Source: `benchmarks/` and the README.
+
+## Scoreboard
+
+Render plain ASCII bars. The bar length shows the measured range; the label
+carries the exact figure:
+
+```
+  ponytail gain                     benchmark median · 5 tasks · 3 models
+
+  Lines of code   no-skill  ████████████████████  100%
+                  ponytail  ██▌·················    6–20%   ▼ 80–94%
+  Cost            no-skill  ████████████████████  100%
+                  ponytail  █████▌··············   23–53%  ▼ 47–77%
+  Speed           ponytail  ▸ 3–6× faster
+
+  This repo:  /ponytail-debt  (shortcuts you deferred)
+              /ponytail-audit (what's still cuttable)
+```
+
+## Honesty boundary
+
+These are benchmark medians, not this repo. NEVER print a per-repo savings
+number ("you saved X lines/tokens here"): the unbuilt version was never
+written, so there is no real baseline to subtract from in a live repo. The
+only real per-repo figures come from `/ponytail-debt` (a counted ledger), and
+this card points there instead of inventing one.
+
+## Boundaries
+
+One-shot display. Edits nothing, changes no mode.
+"stop ponytail" or "normal mode": revert.

skills/ponytail-help/SKILL.md

@@ -27,6 +27,7 @@ Level sticks until changed or session end.
 |-------|---------|--------------|
 | **ponytail** | `/ponytail` | Lazy mode itself. Simplest solution that works. |
 | **ponytail-review** | `/ponytail-review` | Over-engineering review: `L42: yagni: factory, one product. Inline.` |
+| **ponytail-gain** | `/ponytail-gain` | Measured-impact scoreboard: less code, less cost, more speed. |
 | **ponytail-help** | `/ponytail-help` | This card. |
 
 Codex uses `@ponytail`, `@ponytail-review`, and `@ponytail-help`; Claude Code