chore: add module, license and repository guides

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

AGENTS.md

@@ -0,0 +1,9 @@
+# AGENTS.md
+
+Go module `go.auvem.com/corestack`. Reading map:
+
+- Build and test: `go build ./...`, `go vet ./...`, `go test -race ./...`; format with `gofmt -w .`.
+- Docs format (the spec `docs check` implements): `docs/docs-format.md`.
+- Check records: `go run ./cmd/docs check`. Create one: `go run ./cmd/docs new adr|plan "Title"`.
+- Decisions live in `docs/adr/`, plans in `docs/plans/`. Records are permanent; never rename them.
+- Dependencies are limited to `go.yaml.in/yaml/v3` and `github.com/yuin/goldmark`.