docs(portal-self-service): frontend-decisions + demo note for S-08a (refs #65)

Record the workspace/tooling decisions (pnpm, Nx scoped to apps/+libs/, Vitest,
no @nx/docker, no Nx Cloud, Gitea-only) and a demo note for running the placeholder
app. NL DS deferred to S-08c.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/demo-script.md

@@ -5,6 +5,27 @@ copy-pasteable walkthrough against a local `make up` stack.
 
 ---
 
+## S-08a — Nx workspace + self-service portal skeleton
+
+**Outcome:** the frontend foundation — an Nx (pnpm) monorepo with the `self-service` Angular app
+(standalone + signals), lint/test/build green in a CI Node lane. The login + submit form follow in
+S-08c.
+
+```bash
+# From a fresh clone (Node 24 + pnpm 11):
+pnpm install                       # native builds are pre-approved in pnpm-workspace.yaml
+pnpm nx test self-service          # Vitest component test
+pnpm nx build self-service         # production build
+pnpm nx serve self-service         # → http://localhost:4200  (placeholder page)
+# Or the CI-equivalent one-shot:
+make frontend                      # install + nx lint/test/build
+```
+
+> Nx manages only `apps/`+`libs/`; the .NET services stay on `dotnet`/the Makefile. NL Design System
+> and the real form arrive in S-08c (#67); see `docs/frontend-decisions.md`.
+
+---
+
 ## S-07 — BFF: the portals' single backend
 
 **Outcome:** the BFF validates Keycloak `digid` tokens on the self-service submit (forwarding the