chore: add AGENTS.md with E2E test rules

.cursorrules

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+AGENTS.md

AGENTS.md

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+# Repository AI Guidelines
+
+Before adding to this file, carefully consider that poorly written AGENTS.md files can hurt task success rates, while also increasing token usage.
+
+## E2E Testing Guidelines (`test/openshift/e2e/ginkgo/**/*`)
+
+When creating or modifying Ginkgo E2E test files:
+
+### General Guidelines
+
+- **Avoid `k8sClient.Update(...)`**: This call will occasionally fail due to Kubernetes resources being modified between the Get and Update calls.
+  - Instead, use fixture-specific `Update` functions. Most fixture packages include an `Update` function, for example for `ArgoCD` CR: use `argocdFixture.Update(...)`. For generic resource update, see `k8sFixture.Update(...)`.
+
+### Parallel Tests (`test/openshift/e2e/ginkgo/parallel/*_test.go`)
+
+- Use `Describe("GitOps Operator Parallel E2E Tests", func() { ... })` as the top-level describe block
+- Call `fixture.EnsureParallelCleanSlate()` in the `BeforeEach` function. (not `EnsureSequentialCleanSlate`)
+
+### Sequential Tests (`test/openshift/e2e/ginkgo/sequential/*_test.go`)
+
+- Use `Describe("GitOps Operator Sequential E2E Tests", func() { ... })` as the top-level describe block
+- Call `fixture.EnsureSequentialCleanSlate()` in the `BeforeEach` function. (not `EnsureParallelCleanSlate`)

CLAUDE.md

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+AGENTS.md