skill: make the peltier skill consumable across agent harnesses

The SKILL.md Agent Skills standard (agentskills.io) is now read natively by
Codex, Copilot, VS Code, Cursor, Gemini CLI, opencode, Goose, Amp, Zed,
Factory, and ZeroClaw — so the portable move is not per-harness adapter
files (forked content that drifts) but one canonical skill placed where
each harness actually looks.

- Spec-compliant frontmatter: license, compatibility (the Linux-only
  measurement story, stated up front), version/author/tags top-level
  (ZeroClaw's runtime reads those; the spec ignores unknown fields).
  reference/ renamed to references/ per the spec's conventional layout.
- .agents/skills/peltier/ mirror: the cross-tool convergence path (Codex,
  Zed, Cursor, Gemini CLI, Copilot, opencode, Goose, Amp). Byte-identical
  to the .claude canonical, enforced by CI — drift between the two copies
  is a red build, not a footnote.
- AGENTS.md at the repo root for the ~20 harnesses that read it (Claude
  Code does not; CLAUDE.md remains its file). Deliberately thin: it points
  at CLAUDE.md and the skill instead of restating rules.
- scripts/install-skill.sh: stamps a consumer repo at both discovery paths
  (--layout claude|agents|both), or emits a script-less --zeroclaw-variant.
  ZeroClaw's skill security policy blocks script files by default
  (skills.allow_scripts off) — its audit rejected the full skill and passes
  the variant, verified against the real zeroclaw binary. The variant loses
  nothing: preflight.sh still exists exactly once, in the peltier checkout
  the skill already requires, and SKILL.md now documents running it from
  there. Re-implementing preflight inline is named as a refusal condition.
- CI (skill-preflight): frontmatter upgraded to a full Agent Skills spec
  conformance check on BOTH copies (name rules, dir match, description and
  body limits, metadata string-map), plus mirror equality and a functional
  installer test (both layouts identical to canonical, variant carries no
  scripts/, nonexistent target refused).

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

AGENTS.md

@@ -0,0 +1,33 @@
+# peltier.io — agent entry point
+
+This file exists for AGENTS.md-reading harnesses (Codex, Jules, Cursor, Zed,
+Amp, Copilot coding agent, Gemini CLI, …). It is deliberately thin: the
+binding project rules live in one place, not here.
+
+## Working on this repo
+
+Read **[CLAUDE.md](CLAUDE.md)** first and treat it as binding regardless of
+which harness you are. It holds the non-negotiables (no unverified performance
+claims, measure-before-optimizing, hard equivalence gates, the append-only
+ledger, the trust-layer write boundary) and the honest current state of every
+subsystem. The engineering spec is [SPEC.md](SPEC.md). Commands live in the
+[justfile](justfile). The pipeline is Linux/POSIX-only at runtime; Windows
+compiles the workspace but cannot run it.
+
+Two hard rules that bear repeating even in a pointer file:
+
+- **Never claim a performance number without its confidence interval and
+  workload.** If you did not run the gates, the number does not exist.
+- **The trust layer (`crates/`, `config/`, `corpora/`) is read-only to
+  optimization agents.** Patches touch only allowlisted paths under
+  `targets/<name>/`.
+
+## Verifying performance changes (any repo, any harness)
+
+This repo ships its trust layer as an Agent Skill:
+**[.claude/skills/peltier/SKILL.md](.claude/skills/peltier/SKILL.md)** —
+mirrored byte-identically at `.agents/skills/peltier/` for harnesses that
+discover skills there (CI enforces the mirror). If your harness auto-loads
+skills from either path, use it whenever a task involves proving or refuting
+a speedup. If not, read that SKILL.md and follow it manually — starting with
+`scripts/preflight.sh`, whose refusal is final.