improve: add missing AGENTS.md for agent workflow conventions

Author: dev-engineer

AGENTS.md

@@ -0,0 +1,13 @@
+# deadcode
+
+Repo guide for agents.
+
+## Workflow
+- Use `pytest` for tests.
+- Use `ruff` for lint/format.
+- Build/publish via GitHub Actions in `.github/workflows/`.
+
+## Conventions
+- Package code under `src/deadcode` per `pyproject.toml` packaging config.
+- Keep branches `improve/<repo>-<timestamp>` for structural fixes.
+- Do not modify dependencies without updating `pyproject.toml`.