docs(arch): ADR-0008 read projection store + demo note for the event path (refs #7)

ADR-0008 records the read-projection design: one rebuildable store shared by the Event
Subscriber (writer) and projection-api (reader) as one CQRS bounded context (reconciled
with §8.5), idempotency + rebuild from the notification log (no OpenZaak access, §8.1),
the deferred bsn/naam, and the new EF Core + Npgsql dependency. Add a demo-script entry
walking the OZ→NRC→subscriber→projection-api path and wire both into the MkDocs nav.

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

mkdocs.yml

@@ -29,7 +29,9 @@ nav:
       - "ADR-0005: Mutation testing": architecture/adr-0005-mutation-testing.md
       - "ADR-0006: ACL integration test provisioning": architecture/adr-0006-integration-test-provisioning.md
       - "ADR-0007: OpenZaak → NRC notification wiring": architecture/adr-0007-notification-wiring.md
+      - "ADR-0008: Read projection store": architecture/adr-0008-read-projection-store.md
   - Working in Gitea: gitea-workflow.md
+  - Demo script: demo-script.md
   - Runbooks:
       - CI: runbooks/ci.md