feat(central): one central cache-invalidation topic; role-mapping and external-definition caches follow peer edits (ScadaBridge#100 item 3, ScadaBridge#83)

The #96 site-psk-invalidation topic was the first cross-node invalidation broadcast.
It is generalised into ONE central DistributedPubSub topic, central-cache-invalidation,
carrying typed messages (Commons ICentralCacheInvalidation: SitePskInvalidated,
RoleMappingsInvalidated, ExternalDefinitionsInvalidated, InboundApiMethodInvalidated)
in an envelope stamped with the publisher's process-unique origin id.

- Host: CentralCacheInvalidationBus (ICentralCacheInvalidationPublisher, no-op until
  the mediator is set, never throws) and CentralCacheInvalidationSubscriber, which
  skips its own node's envelopes and hands the peer's to every registered
  ICentralCacheInvalidationHandler (a failing handler does not stop the rest).
  Replaces SitePskInvalidationSubscriber.
- Migration of #96: SitePskRotationInvalidator publishes through the bus and is the
  PSK handler; SitePskInvalidated keeps its type name and is also published bare on
  site-psk-invalidation, which the subscriber still listens to, so a mixed-version
  central pair keeps exchanging PSK invalidations. Remove after one release.
- Audit D1: RoleMappingCache is a handler; ManagementActor's post-commit role-mapping
  invalidation also publishes RoleMappingsInvalidated, so a revocation is immediate on
  the peer instead of after RoleMappingCacheSeconds.
- Audit D3 / #83 (peer half): ExternalDefinitionLookupCache is a handler; the 9
  ManagementActor handlers and the Transport bundle importer publish
  ExternalDefinitionsInvalidated after commit. (#83's local import half was already in.)

TTLs remain the fallback for a lost broadcast or a direct SQL edit. Tests: bus and
subscriber unit tests (origin filter, legacy topic), peer-node tests through the real
caches in ManagementService.Tests, importer publish, composition root, and a real
two-node cluster from the production HOCON (CentralCacheInvalidationTwoNodeTests)
proving every message type crosses with the production serializer. Docs: Host,
Communication, Security, ManagementService, ESG, and the #85 cache audit.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

src/ZB.MOM.WW.ScadaBridge.Host/Program.cs

@@ -413,7 +413,10 @@ try
         builder.Services.AddScadaBridgeSecrets(builder.Configuration, SecretsNodeRole.Central);
         // An in-place rotation of a site's SB-GRPC-PSK-{siteId} through /admin/secrets must drop
         // central's cached copy of that key on BOTH central nodes (Gitea #96). Wraps the library's
-        // ISecretCacheInvalidator; the peer half is wired in AkkaHostedService.RegisterCentralActors.
+        // ISecretCacheInvalidator; the peer half rides the central cache-invalidation topic
+        // (AddCentralCacheInvalidation, ScadaBridge#100 item 3 — also used by the role-mapping,
+        // external-definition and inbound-API caches), wired in AkkaHostedService.RegisterCentralActors.
+        builder.Services.AddCentralCacheInvalidation();
         builder.Services.AddSitePskRotationInvalidation();
         // Secrets UI authorization: adds the named policies secrets:manage + secrets:reveal
         // (role-based) consumed by the /admin/secrets page. AddSecretsAuthorization only ADDS