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.Infrastructure/OpenZaakGateway.cs

@@ -142,6 +142,48 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         return created;
     }
 
+    public async Task<Uri> ResolveZaaktypeUrlAsync(string identificatie, CancellationToken ct = default)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(identificatie);
+
+        // The published zaaktype with this identificatie; status=definitief excludes concepts.
+        var page = await GetAsync<ZaaktypePage>(
+            "/catalogi/api/v1/zaaktypen?status=definitief&identificatie=" + Uri.EscapeDataString(identificatie),
+            "zaaktypen", ct);
+        var match = (page.Results ?? []).FirstOrDefault()
+            ?? throw new InvalidOperationException(
+                $"No published zaaktype with identificatie '{identificatie}' found in OpenZaak — is the BIG catalogus seeded and published?");
+        return new Uri(match.Url);
+    }
+
+    public async Task<Uri> ResolveInformatieobjecttypeUrlAsync(string omschrijving, CancellationToken ct = default)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(omschrijving);
+
+        // The informatieobjecttypen collection has no omschrijving filter, so match client-side over the
+        // published ones.
+        var page = await GetAsync<InformatieobjecttypePage>(
+            "/catalogi/api/v1/informatieobjecttypen?status=definitief", "informatieobjecttypen", ct);
+        var match = (page.Results ?? []).FirstOrDefault(i => i.Omschrijving == omschrijving)
+            ?? throw new InvalidOperationException(
+                $"No published informatieobjecttype '{omschrijving}' found in OpenZaak — is the BIG catalogus seeded and published?");
+        return new Uri(match.Url);
+    }
+
+    // GETs an absolute-by-path ZGW resource with auth (no CRS — catalogi is not a geo API).
+    private async Task<T> GetAsync<T>(string pathAndQuery, string label, CancellationToken ct)
+    {
+        using var message = new HttpRequestMessage(HttpMethod.Get, new Uri(options.BaseUrl, pathAndQuery));
+        message.Headers.Authorization =
+            new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
+
+        using var response = await http.SendAsync(message, ct);
+        await EnsureSuccessAsync(response, $"Querying {label}", ct);
+
+        return await response.Content.ReadFromJsonAsync<T>(ct)
+            ?? throw new InvalidOperationException($"OpenZaak returned an empty {label} response");
+    }
+
     // POSTs a non-geo ZGW resource (resultaat/status — no CRS headers). Buffers the body so uwsgi gets
     // a Content-Length instead of a chunked body (as with zaak-create).
     private async Task PostAsync(string path, object dto, string action, CancellationToken ct)
@@ -298,4 +340,18 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
     private sealed record ZaakInformatieobjectDto(
         [property: JsonPropertyName("zaak")] string Zaak,
         [property: JsonPropertyName("informatieobject")] string Informatieobject);
+
+    private sealed record ZaaktypePage(
+        [property: JsonPropertyName("results")] IReadOnlyList<ZaaktypeDto>? Results);
+
+    private sealed record ZaaktypeDto(
+        [property: JsonPropertyName("url")] string Url,
+        [property: JsonPropertyName("identificatie")] string? Identificatie);
+
+    private sealed record InformatieobjecttypePage(
+        [property: JsonPropertyName("results")] IReadOnlyList<InformatieobjecttypeDto>? Results);
+
+    private sealed record InformatieobjecttypeDto(
+        [property: JsonPropertyName("url")] string Url,
+        [property: JsonPropertyName("omschrijving")] string? Omschrijving);
 }