test(event-subscriber): project zaak-created notifications into the read projection (refs #7)

Failing unit + acceptance tests for the Event Subscriber's NotificationProjector:
a zaken/zaak/create notification yields one INGEDIEND projection row, duplicate
deliveries collapse to one row, non-zaak/non-create notifications are ignored, and
a rebuild repopulates the projection from the durable notification log (PRD §8.4).

The projector is a no-op stub so the tests compile and fail on the assertions; the
implementation follows in the green commit. The notification log doubles as the
idempotency guard and rebuild source so a rebuild needs no OpenZaak access (§8.1).

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

services/event-subscriber/EventSubscriber.Application/NotificationProjector.cs

@@ -0,0 +1,19 @@
+namespace EventSubscriber.Application;
+
+/// <summary>
+/// Projects inbound NRC notifications into the read projection. Tolerates duplicate and
+/// out-of-order deliveries (CLAUDE.md §8.6): the notification log dedups, and the projection
+/// upsert is idempotent on the zaak id. Rebuilds the projection by replaying the log.
+/// </summary>
+public sealed class NotificationProjector(INotificationLog log, IProjectionStore store)
+{
+    /// <summary>Handle one inbound notification. Ignores anything that is not a zaak-created event.</summary>
+    public Task HandleAsync(Notification notification, CancellationToken ct = default)
+        // RED: not yet implemented — the smallest change to make the tests pass comes next.
+        => Task.CompletedTask;
+
+    /// <summary>Rebuild the projection from the durable notification log (PRD §8.4).</summary>
+    public Task RebuildAsync(CancellationToken ct = default)
+        // RED: not yet implemented.
+        => Task.CompletedTask;
+}