feat(workflow): escalation drain loop reassigns then completes (S-14, refs #15)

Implement BeoordelingEscalatieProcessor.PumpOnceAsync over the escalation client.

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

services/domain/Big.Infrastructure/BeoordelingEscalatieProcessor.cs

@@ -14,6 +14,24 @@ public sealed class BeoordelingEscalatieProcessor(
     ILogger<BeoordelingEscalatieProcessor> logger)
 {
     /// <summary>Acquire and process up to <paramref name="maxJobs"/> escalations. Returns the number acquired.</summary>
-    public Task<int> PumpOnceAsync(int maxJobs, CancellationToken ct = default)
-        => throw new NotImplementedException();
+    public async Task<int> PumpOnceAsync(int maxJobs, CancellationToken ct = default)
+    {
+        var jobs = await client.AcquireBeoordelingEscalatieJobsAsync(maxJobs, ct);
+
+        foreach (var job in jobs)
+        {
+            try
+            {
+                await client.ReassignBeoordelingToTeamleadAsync(job.ProcessInstanceId, ct);
+                await client.CompleteBeoordelingEscalatieJobAsync(job.JobId, ct);
+            }
+            catch (Exception ex)
+            {
+                // Leave the job un-completed: its lock expires and Flowable redelivers it (§8.6).
+                logger.LogError(ex, "BeoordelingEscaleren job {JobId} failed; leaving it for redelivery.", job.JobId);
+            }
+        }
+
+        return jobs.Count;
+    }
 }