test(workflow): beoordeling escalation reassigns to teamlead (S-14, refs #15)

Failing Workflow Client tests for the 14-day escalation capability (ADR
proposal #98): acquire BeoordelingEscaleren external-worker jobs, reassign the
still-open Beoordelen task's candidate group behandelaar -> teamlead, and
complete the escalation job. Methods are stubbed to throw so the suite compiles
and fails on the new behaviour only.

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

services/domain/Big.Infrastructure/FlowableWorkflowClient.cs

@@ -106,6 +106,15 @@ public sealed class FlowableWorkflowClient(HttpClient http, FlowableOptions opti
         response.EnsureSuccessStatusCode();
     }
 
+    public Task<IReadOnlyList<EscalatieJob>> AcquireBeoordelingEscalatieJobsAsync(int maxJobs, CancellationToken ct = default)
+        => throw new NotImplementedException();
+
+    public Task ReassignBeoordelingToTeamleadAsync(string processInstanceId, CancellationToken ct = default)
+        => throw new NotImplementedException();
+
+    public Task CompleteBeoordelingEscalatieJobAsync(string jobId, CancellationToken ct = default)
+        => throw new NotImplementedException();
+
     private async Task<TResponse?> GetAsync<TResponse>(string path, CancellationToken ct)
     {
         var message = new HttpRequestMessage(HttpMethod.Get, new Uri(options.BaseUrl, path));