feat(portal-beheer): beheer portal + read-only catalogus viewer (closes #130) (#133)

## What & why

S-15a, the first of the S-15 (#16) split. A new **beheer** portal (medewerker realm, like behandel) shows the ZTC catalogus — the published zaaktypen — **read-only**. A beheerder logs in and sees the seeded BIG-REGISTRATIE zaaktype.

Closes #130

### The vertical

portal → BFF `GET /beheer/catalogi/zaaktypen` (medewerker realm + `beheerder` role) → ACL `GET /catalogi/zaaktypen` → ZGW Catalogi API.

- **ACL**: new read-only `GET /catalogi/zaaktypen` listing published zaaktypen (reuses the ADR-0021 Catalogi client; public-safe `identificatie`/`omschrijving`).
- **BFF**: new typed `IAclClient` + `Downstream:Acl:BaseUrl`, and `GET /beheer/catalogi/zaaktypen` behind a new `beheerder` policy (reuses the medewerker bearer scheme + realm-role lifting). OpenAPI spec + generated Angular client regenerated.
- **Keycloak**: `beheerder` realm role + `bram-beheerder` test user in the medewerker realm.
- **Frontend**: new `apps/beheer` Angular app (copied from behandel) with a read-only catalogus page; `SECURE_API_ROUTES=['/beheer/']`.
- **Infra**: `beheer` compose service (port 8143), added to `WAIT_SVCS` + CI log-dump; a Playwright e2e (beheerder login → catalogus shows BIG-REGISTRATIE).

### New boundary → ADR-0025

The BFF now reaches the **ACL directly** for the catalogus read — a new service-to-service edge (§14). The catalogus is neither a domain nor a projection concern, and §8.1 means only the ACL may read ZGW; routing through the domain would pollute it with a non-domain passthrough. §8.1/§8.3 stay intact. Recorded in **ADR-0025**.

## Definition of Done

- [x] Failing test committed before each implementation (red→green per layer: ACL, BFF, frontend).
- [x] Conventional Commits referencing #130.
- [ ] CI green — pending Gitea Actions run.
- [x] `docker compose up` brings up `beheer` (health-gated in `WAIT_SVCS`).
- [x] Docs — ADR-0025 + demo-script S-15a note.
- [x] Demo note in `docs/demo-script.md`.

## Verified locally

lint (`dotnet format`) ✓ · .NET unit (Acl 57 / Big 152 / EventSubscriber 19 / Bff 40) ✓ · frontend lint+test (8 projects) ✓ · frontend build (4 apps) ✓. Mutation ratchet: added a gateway unit test for the new `ListZaaktypenAsync` mapping so the ACL score holds. verify-stack (compose smoke + e2e) runs in CI.

## Notes for reviewers

- The BFF drops the ZGW URL from `BeheerZaaktype` (public-safe: identificatie + omschrijving only).
- The catalogus e2e asserts on the stable seeded `BIG-REGISTRATIE` (not a per-test reference), safe on the shared verify stack.
- Follow-ups: **S-15b** (#131) default-fill CRUD, **S-15c** (#132) medewerker-realm MFA.

🤖 Generated with [Claude Code](https://claude.com/claude-code)Reviewed-on: #133

services/bff/Bff.Api/DownstreamClients.cs

@@ -54,6 +54,19 @@ public interface IProjectionClient
     Task<IReadOnlyList<ProjectionEntry>> GetRegisterAsync(CancellationToken ct = default);
 }
 
+/// <summary>A published zaaktype as the beheer catalogus viewer shows it (S-15a): the business
+/// <c>Identificatie</c> + human <c>Omschrijving</c>. The ZGW URL the ACL also returns is dropped — an
+/// internal reference, not shown in the portal.</summary>
+public sealed record BeheerZaaktype(string Identificatie, string Omschrijving);
+
+/// <summary>Port to the ACL for read-only catalogus queries (beheer portal, S-15a). The BFF reaches the
+/// ACL directly for this read: the catalogus isn't a domain concern, and the ACL is the only code
+/// allowed to read the ZGW Catalogi API (§8.1, ADR-0025).</summary>
+public interface IAclClient
+{
+    Task<IReadOnlyList<BeheerZaaktype>> GetZaaktypenAsync(CancellationToken ct = default);
+}
+
 /// <summary>Calls the Domain Service's <c>POST /registrations</c>.</summary>
 public sealed class DomainClient(HttpClient http) : IDomainClient
 {
@@ -121,3 +134,11 @@ public sealed class ProjectionClient(HttpClient http) : IProjectionClient
     public async Task<IReadOnlyList<ProjectionEntry>> GetRegisterAsync(CancellationToken ct = default)
         => await http.GetFromJsonAsync<List<ProjectionEntry>>("register", ct) ?? [];
 }
+
+/// <summary>Calls the ACL's <c>GET /catalogi/zaaktypen</c> (S-15a). The ACL also returns each zaaktype's
+/// ZGW URL; deserializing into <see cref="BeheerZaaktype"/> keeps only the public-safe fields.</summary>
+public sealed class AclClient(HttpClient http) : IAclClient
+{
+    public async Task<IReadOnlyList<BeheerZaaktype>> GetZaaktypenAsync(CancellationToken ct = default)
+        => await http.GetFromJsonAsync<List<BeheerZaaktype>>("catalogi/zaaktypen", ct) ?? [];
+}