feat(acl): resolve the zaaktype by identificatie, not a pinned URL (S-27, closes #113) (#118)

## What & why

The ACL was handed a **pinned zaaktype URL** (`Acl__Defaults__ZaaktypeUrl`) + informatieobjecttype URL. OpenZaak assigns those UUIDs at creation, so every stack had to seed the catalogus and then capture + inject the resulting URLs out of band (CI's `run-domain-check.sh`; the local `local-seed`→`acl.env` bootstrap from ADR-0020). Brittle, and a stale/placeholder URL failed opaquely (OpenZaak 400).

Now **the ACL resolves them itself** from OpenZaak's Catalogi API by stable business key:
- config `ZaaktypeIdentificatie` (`BIG-REGISTRATIE`) / `InformatieobjecttypeOmschrijving` (`Diploma`);
- a `CachedZaaktypeCatalog` resolves **lazily on first use** and caches (success only, so a pre-publish miss is retried — no startup ordering coupling);
- a clear "No published … found" error replaces the opaque placeholder 400.

Design in **ADR-0021** (proposed in #117).

Closes #113
Closes #117

## Consequences (the payoff)

No stack captures/injects a server-assigned URL any more — `docker-compose.yml`/`.local.yml`, `run-domain-check.sh` and `local-seed` all drop it; the local `acl.env` shrinks to a single line.

**One thing S-27 can't remove** (confirmed empirically during this work): OpenZaak validates the `zaaktype` field on zaak-create with Django's URLValidator and **rejects a single-label host** (`http://openzaak:8000/…` → `zaaktype: bad-url`). So the ACL's **base URL** must still point at a URL-valid host (a container IP); that base-URL injection from ADR-0020 stays (local `acl.env` now carries only it; CI keeps `ACL_OPENZAAK_BASEURL`). ADR-0021 records this.

## Definition of Done

- [x] Linked issues (#113 slice, #117 adr-proposal).
- [x] TDD — resolver + gateway-lookup unit tests, updated `AclService` tests (50 unit tests green).
- [x] Implementation makes them pass; refactor of both compose stacks + verify scripts follows.
- [x] Conventional Commits referencing #113.
- [ ] CI green — see below.
- [x] `docker compose up` reaches green health — verified: fresh `make local` + `make verify-local` green with **no zaaktype-URL injection**; `acl.env` is base-URL-only.
- [x] Docs — ADR-0021 + demo-script S-27 note.
- [x] ADR added (ADR-0021).
- [x] Demo note appended.

## Verification done locally

- **50 unit tests** pass (resolver resolve/cache/retry-on-failure; gateway match/miss/blank-key; all `AclService` paths).
- **6 ACL integration tests** pass against a live seeded OpenZaak — incl. resolving the zaaktype + Diploma iot by business key, and a clear error for an unknown identificatie.
- **Fresh `make local` + `make verify-local`**: full flow (submit → werkbak → openbaar) green; `acl.env` = `Acl__OpenZaak__BaseUrl` only.
- `make lint` clean; ACL mutation ratchet run locally (see checks).

## Notes for reviewers

- `IZaakGateway` gains two resolve methods; `AclService` depends on the new `IZaaktypeCatalog` (singleton, so the cache persists).
- Supersedes the pinned-URL mechanism; ADR-0021 documents that ADR-0020's `seed-env`/entrypoint shim are **simplified** (base-URL only), not deleted, because of the URLValidator constraint above.

Reviewed-on: #118

services/acl/Acl.IntegrationTests/OpenZaakGatewayIntegrationTests.cs

@@ -161,4 +161,32 @@ public sealed class OpenZaakGatewayIntegrationTests(OpenZaakFixture stack)
         Assert.Contains(relations.EnumerateArray(),
             r => r.GetProperty("zaak").GetString() == zaakUrl.ToString());
     }
+
+    [Fact]
+    public async Task Resolves_the_published_zaaktype_and_diploma_informatieobjecttype_by_business_key()
+    {
+        var expectedZaaktype = await stack.FindPublishedBigZaaktypeAsync();
+        Assert.True(expectedZaaktype is not null,
+            "No published BIG-REGISTRATIE zaaktype found — seed the stack with OZ_PUBLISH=1.");
+        var expectedInformatieobjecttype = await stack.FindPublishedDiplomaInformatieobjecttypeAsync();
+        Assert.True(expectedInformatieobjecttype is not null,
+            "No published Diploma informatieobjecttype found — seed the stack with OZ_PUBLISH=1.");
+
+        var gateway = new OpenZaakGateway(stack.Http, stack.Options);
+
+        // The ACL discovers both URLs from the live Catalogi API by their stable business keys (S-27),
+        // matching what the fixture found independently — no pinned URL needed.
+        Assert.Equal(expectedZaaktype, await gateway.ResolveZaaktypeUrlAsync("BIG-REGISTRATIE"));
+        Assert.Equal(expectedInformatieobjecttype, await gateway.ResolveInformatieobjecttypeUrlAsync("Diploma"));
+    }
+
+    [Fact]
+    public async Task Resolving_an_unknown_zaaktype_identificatie_throws_a_clear_error()
+    {
+        var gateway = new OpenZaakGateway(stack.Http, stack.Options);
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(
+            () => gateway.ResolveZaaktypeUrlAsync("NO-SUCH-ZAAKTYPE"));
+        Assert.Contains("NO-SUCH-ZAAKTYPE", ex.Message);
+    }
 }