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>

register-referentie.slnx

@@ -12,9 +12,14 @@
     <Project Path="services/bff/Bff.Tests/Bff.Tests.csproj" />
   </Folder>
   <Folder Name="/services/event-subscriber/">
+    <Project Path="services/event-subscriber/EventSubscriber.Api/EventSubscriber.Api.csproj" />
     <Project Path="services/event-subscriber/EventSubscriber.Application/EventSubscriber.Application.csproj" />
     <Project Path="services/event-subscriber/EventSubscriber.Tests/EventSubscriber.Tests.csproj" />
   </Folder>
+  <Folder Name="/services/projection-api/">
+    <Project Path="services/projection-api/Projection.ReadModel/Projection.ReadModel.csproj" />
+    <Project Path="services/projection-api/ProjectionApi.Api/ProjectionApi.Api.csproj" />
+  </Folder>
   <Folder Name="/tests/">
     <Project Path="tests/acceptance/Acceptance.csproj" />
   </Folder>