docs: добавлен AGENTS.md для orientation AI-агентов

- Зачем:
  - конвенция AGENTS.md (codex, aider и др. агенты её автодетектят) даёт свежему агенту быструю навигацию по репо без прочтения всех 50 KB DESIGN.md перед началом работы.
- Что:
  - Короткий (~25 строк) pointer-файл: one-paragraph what-is-this, три main-docs с one-line описанием, три "don't"-правила про cross-refs / session marker / silent-recovery, верификация через §7 smoke-test + dogfood.
  - Всё содержательное остаётся в DESIGN.md; AGENTS.md только ориентирует.
- Проверка:
  - Файл существует, читаем, ссылается на реальные §-номера в DESIGN.md (§4.1b, §6.7, §6.8, §7, §9.6, §10).

AGENTS.md

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+# AGENTS.md
+
+Orientation for AI coding agents working on this repo.
+
+## What this is
+
+A Claude Code skill that orchestrates adversarial review: Claude writes an adversarial prompt, launches OpenAI Codex as an external reviewer, shows the findings to the user, applies fixes, and iterates up to 5 rounds until approved. This is **not a regular codebase** — the product is a single instruction file (`SKILL.md`) executed by Claude Opus at runtime.
+
+## Where to look
+
+- **README.md** — user-facing: install, permissions, troubleshooting.
+- **SKILL.md** — the instruction template Opus executes. Uses `${PLACEHOLDER}` syntax for runtime substitution (not shell variables). Step ordering is load-bearing.
+- **docs/DESIGN.md** — the "why" behind every non-obvious decision, rejected alternatives, verification protocol (§7 smoke tests), and the update protocol (§10). Read §10 before modifying SKILL.md.
+- **examples/** — sample outputs. Not source of truth.
+
+## Before you change things
+
+- Don't renumber DESIGN.md sections — cross-refs across all three files break silently (§10.2).
+- Don't remove the session marker `<!-- ADVERSARIAL-REVIEW-SESSION: ${REVIEW_ID}-${ATTEMPT_ID} -->` from prompt templates — the session-id fallback depends on it (§4.1b).
+- Don't add silent-recovery fallbacks. The skill's explicit preference is fail-closed over masked failure (§6.7, §6.8).
+
+## Verifying a change
+
+- Smoke test: `docs/DESIGN.md §7` — copy-paste bash, runs in ~2 minutes.
+- End-to-end: dogfood via `/adversarial-review code` against any branch with commits vs master.
+- No automated CI (§9.6 explains why).