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/acl/Acl.Tests/OpenZaakGatewayTests.cs

@@ -824,4 +824,51 @@ public class OpenZaakGatewayTests
         await Assert.ThrowsAnyAsync<ArgumentException>(() => Gateway(handler).ResolveZaaktypeUrlAsync(" "));
         await Assert.ThrowsAnyAsync<ArgumentException>(() => Gateway(handler).ResolveInformatieobjecttypeUrlAsync(" "));
     }
+
+    [Fact]
+    public async Task Listing_zaaktypen_queries_published_zaaktypen_and_maps_them(/* S-15a */)
+    {
+        HttpRequestMessage? seen = null;
+        var handler = new StubHandler(req =>
+        {
+            seen = req;
+            const string json = """
+                {"results":[
+                  {"url":"http://openzaak/catalogi/api/v1/zaaktypen/big","identificatie":"BIG-REGISTRATIE","omschrijving":"BIG-registratie"},
+                  {"url":"http://openzaak/catalogi/api/v1/zaaktypen/her","identificatie":"BIG-HERREGISTRATIE","omschrijving":"BIG-herregistratie"}
+                ]}
+                """;
+            return Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK)
+            {
+                Content = new StringContent(json, Encoding.UTF8, "application/json"),
+            });
+        });
+
+        var zaaktypen = await Gateway(handler).ListZaaktypenAsync();
+
+        // Only the published zaaktypen collection is queried (status=definitief excludes concepts).
+        Assert.Contains("/catalogi/api/v1/zaaktypen", seen!.RequestUri!.ToString());
+        Assert.Contains("status=definitief", seen.RequestUri!.ToString());
+        // Authenticated like the other catalogi reads.
+        Assert.Equal("Bearer", seen.Headers.Authorization!.Scheme);
+        // Each result maps to a public-safe summary (identificatie + omschrijving + url).
+        Assert.Equal(2, zaaktypen.Count);
+        Assert.Equal("BIG-REGISTRATIE", zaaktypen[0].Identificatie);
+        Assert.Equal("BIG-registratie", zaaktypen[0].Omschrijving);
+        Assert.Equal(new Uri("http://openzaak/catalogi/api/v1/zaaktypen/big"), zaaktypen[0].Url);
+        Assert.Equal("BIG-HERREGISTRATIE", zaaktypen[1].Identificatie);
+    }
+
+    [Fact]
+    public async Task Listing_zaaktypen_returns_empty_when_the_catalogus_has_none()
+    {
+        var handler = new StubHandler(_ => Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK)
+        {
+            Content = new StringContent("""{"results":[]}""", Encoding.UTF8, "application/json"),
+        }));
+
+        var zaaktypen = await Gateway(handler).ListZaaktypenAsync();
+
+        Assert.Empty(zaaktypen);
+    }
 }