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

docs/requirements/Component-Host.md

@@ -351,5 +351,6 @@ built)* section for where the shipped code deviates from the original design).
 - **Port options come from the bound `NodeOptions`.** `Program.cs` binds `ScadaBridge:Node` once and reads `GrpcPort` / `CentralGrpcPort` / `MetricsPort` from it; the 8083/8084 defaults live only in `NodeOptions`. Central's dedicated metrics listener remains an explicit *presence* check on the raw key (a defaulted read would bind a new port on every existing central node).
 - **Inbound method warm-up is a hosted service** (`InboundMethodWarmupService`, registered after `AkkaHostedService`), not a pre-`RunAsync` loop — see Component-InboundAPI.md.
 - **`SitePskProvider` distinguishes a secret-store fault from a missing secret.** A store fault logs a Warning with the exception and throws `SecretStoreUnavailableException` (not cached); only a genuinely absent/empty/tombstoned secret produces the "seed `SB-GRPC-PSK-{site}`" message.
-- **`SitePskProvider`'s cache follows an in-place rotation (Gitea #96).** Central replaces the secrets library's `ISecretCacheInvalidator` with `SitePskRotationInvalidator` (`AddSitePskRotationInvalidation`), which drops the site's cached key when `SB-GRPC-PSK-{site}` is written and publishes `SitePskInvalidated` on the `site-psk-invalidation` `DistributedPubSub` topic; `AkkaHostedService.RegisterCentralActors` starts the `SitePskInvalidationSubscriber` that applies the peer's broadcasts. A site's auth rejection and a `SitePsks` reload also drop the cache — see Component-Communication.md → *Authentication*.
+- **`SitePskProvider`'s cache follows an in-place rotation (Gitea #96).** Central replaces the secrets library's `ISecretCacheInvalidator` with `SitePskRotationInvalidator` (`AddSitePskRotationInvalidation`), which drops the site's cached key when `SB-GRPC-PSK-{site}` is written and publishes `SitePskInvalidated` to the peer over the central cache-invalidation topic (below). A site's auth rejection and a `SitePsks` reload also drop the cache — see Component-Communication.md → *Authentication*.
+- **Central cache invalidation (ScadaBridge#100 item 3).** One `DistributedPubSub` topic, `central-cache-invalidation`, carries typed `ICentralCacheInvalidation` messages (Commons `Messages/Communication/CentralCacheInvalidations.cs`) between the two central nodes, each wrapped in a `CentralCacheInvalidationEnvelope` stamped with the publishing process's origin id. `AddCentralCacheInvalidation` registers `CentralCacheInvalidationBus` as `ICentralCacheInvalidationPublisher`; `AkkaHostedService.RegisterCentralActors` gives it the mediator and starts `CentralCacheInvalidationSubscriber`, which skips its own node's envelopes and hands the peer's to every registered `ICentralCacheInvalidationHandler`: `SitePskRotationInvalidator` (`SitePskInvalidated`, #96), `RoleMappingCache` (`RoleMappingsInvalidated`, audit D1), and `ExternalDefinitionLookupCache` (`ExternalDefinitionsInvalidated`, audit D3 / #83). Publishers invalidate locally first, post-commit, then publish; delivery is best-effort, so each cache's TTL or revision check stays the fallback. Migration: the #96 topic `site-psk-invalidation` is still published to (bare `SitePskInvalidated`) and subscribed, so a briefly mixed-version central pair keeps exchanging PSK invalidations — remove it once every central node runs this build.
 - Central registers `ExternalSystemGatewayOptions.DefinitionCacheTtl = 10 s` ahead of `AddExternalSystemGateway()` so an explicit config value wins; sites leave it off.