chore: add Cursor Cloud environment

.cursor/environment.json

@@ -0,0 +1,4 @@
+{
+  "name": "operator-os-explainer",
+  "install": "set -eu; corepack enable; corepack prepare pnpm@11.15.0 --activate; pnpm install --frozen-lockfile"
+}

AGENTS.md

@@ -0,0 +1,24 @@
+# Operator OS Explainer instructions
+
+## Cursor Cloud specific instructions
+
+This repository is a public, fixture-backed web explainer and is safe to work on in
+an isolated Ubuntu cloud checkout. Setup is defined in `.cursor/environment.json`
+and must remain reproducible from the committed `pnpm-lock.yaml` without secrets,
+local absolute paths, or sibling repositories.
+
+Use Node 22.22 or 24 and the pinned pnpm version. For ordinary changes, verify:
+
+```sh
+pnpm typecheck
+pnpm test
+pnpm build
+pnpm guard
+pnpm generate && git diff --exit-code -- src/data/dataset.json
+pnpm diagrams && git diff --exit-code -- public/diagrams docs/mechanisms.md
+```
+
+Run `pnpm test:e2e` only when browser behavior changes. Keep every displayed
+timeline, project, person, and metric synthetic or explicitly public; do not copy
+private machine state, local portfolio output, credentials, or personal data into
+the repository.