docs: add AGENTS.md with guidelines for AI coding agents

Author: creydr

AGENTS.md

@@ -0,0 +1,31 @@
+# Agent Guidelines
+
+## Project Overview
+
+Kubernetes operator (controller-runtime) for managing middleware updates for serverless functions deployed with the `func` CLI. Written in Go, uses Ginkgo/Gomega for tests.
+
+## Key Commands
+
+- `make test` - unit tests
+- `make test-e2e` - e2e tests (requires Kind cluster with Gitea)
+- `make lint` - run golangci-lint
+- `gofmt` and `goimports` - format Go files after changes
+
+## Project Structure
+
+- `api/v1alpha1/` - Function CRD types
+- `internal/` - controller and business logic
+- `test/e2e/` - e2e tests using in-cluster Gitea
+- `test/utils/` - e2e test helpers (RepositoryProvider, func CLI wrappers)
+- `hack/` - cluster setup scripts
+- `config/` - Kustomize manifests
+
+## Important Documentation
+
+Read these files to understand the project setup, conventions, and development workflow:
+
+- `README.md` - user-facing usage, API reference table, installation
+- `CONTRIBUTING.md` - development setup, workflow, coding conventions
+- `docs/development/` - developer guides (e.g. Gitea integration, test patterns)
+
+After implementing a feature or making significant changes, check whether these docs need updating. The API reference table in README.md must stay in sync with `api/v1alpha1/function_types.go`.