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/ProjectionApi.Api/Program.cs

@@ -0,0 +1,43 @@
+using Microsoft.EntityFrameworkCore;
+using Projection.ReadModel;
+
+var builder = WebApplication.CreateBuilder(args);
+
+var connectionString = builder.Configuration.GetConnectionString("Projection")
+    ?? throw new InvalidOperationException("Missing connection string 'ConnectionStrings:Projection'");
+
+builder.Services.AddProjectionReadModel(connectionString);
+
+var app = builder.Build();
+
+// Ensure the schema exists before serving reads. EF serialises concurrent migrators via the
+// migrations-history lock, so it is safe that the Event Subscriber migrates too.
+await app.Services.MigrateProjectionAsync();
+
+app.MapGet("/health", () => "Healthy");
+
+// The read side of the projection. Public-safe field filtering is tightened in S-09; for now
+// the minimal projection only carries id + status (bsn/naam deferred — ADR-0008).
+app.MapGet("/register", async (ProjectionDbContext db, CancellationToken ct) =>
+{
+    var rows = await db.RegisterEntries
+        .OrderBy(r => r.Id)
+        .Select(r => new RegisterEntryDto(r.Id, r.Status, r.Bsn, r.NaamPlaceholder))
+        .ToListAsync(ct);
+    return Results.Ok(rows);
+});
+
+app.MapGet("/register/{id}", async (string id, ProjectionDbContext db, CancellationToken ct) =>
+{
+    var row = await db.RegisterEntries
+        .Where(r => r.Id == id)
+        .Select(r => new RegisterEntryDto(r.Id, r.Status, r.Bsn, r.NaamPlaceholder))
+        .SingleOrDefaultAsync(ct);
+    return row is null ? Results.NotFound() : Results.Ok(row);
+});
+
+await app.RunAsync();
+
+public sealed record RegisterEntryDto(string Id, string Status, string? Bsn, string? NaamPlaceholder);
+
+public partial class Program;