feat(projection): persist the read projection and expose webhook + read APIs (refs #7)

Add the projection persistence and the two services around it:

- Projection.ReadModel: a shared EF Core (Npgsql) read model owning the projection
  schema — register_projection + the subscriber's processed_notifications log — plus
  EfProjectionStore / EfNotificationLog (atomic record-or-skip on the PK for idempotency)
  and the initial migration. One rebuildable store, written by the subscriber and read
  by projection-api (ADR-0008).
- EventSubscriber.Api: POST /notifications NRC callback (enforces the abonnement bearer,
  401 without it per ADR-0007), POST /admin/rebuild, /health. Migrates on start.
- ProjectionApi.Api: GET /register, GET /register/{id}, /health — the read side.

dotnet-ef pinned as a local tool for migrations; NuGetAuditMode=direct so EF's
design-time-only tooling transitive doesn't flag the shipped build.

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

services/projection-api/Projection.ReadModel/EfProjectionStore.cs

@@ -0,0 +1,40 @@
+using EventSubscriber.Application;
+using Microsoft.EntityFrameworkCore;
+
+namespace Projection.ReadModel;
+
+/// <summary>EF Core implementation of the projection store over <see cref="ProjectionDbContext"/>.</summary>
+public sealed class EfProjectionStore(ProjectionDbContext db) : IProjectionStore
+{
+    public async Task UpsertAsync(RegisterEntry entry, CancellationToken ct = default)
+    {
+        var row = await db.RegisterEntries.FindAsync([entry.Id], ct);
+        if (row is null)
+        {
+            db.RegisterEntries.Add(new RegisterEntryRow
+            {
+                Id = entry.Id,
+                Status = entry.Status,
+                Bsn = entry.Bsn,
+                NaamPlaceholder = entry.NaamPlaceholder,
+            });
+        }
+        else
+        {
+            row.Status = entry.Status;
+            row.Bsn = entry.Bsn;
+            row.NaamPlaceholder = entry.NaamPlaceholder;
+        }
+
+        await db.SaveChangesAsync(ct);
+    }
+
+    public async Task ClearAsync(CancellationToken ct = default)
+        => await db.RegisterEntries.ExecuteDeleteAsync(ct);
+
+    public async Task<IReadOnlyList<RegisterEntry>> AllAsync(CancellationToken ct = default)
+        => await db.RegisterEntries
+            .OrderBy(r => r.Id)
+            .Select(r => new RegisterEntry(r.Id, r.Status, r.Bsn, r.NaamPlaceholder))
+            .ToListAsync(ct);
+}