chore(comm): delete dead IntegrationCallRequest routing (Gitea #32)

'Pattern 4: Integration Routing' — RouteIntegrationCallAsync →
SiteEnvelope(IntegrationCallRequest) → SiteCommunicationActor integration
handler — was plumbed end to end but connected at neither end: no
producer (zero callers) and no handler (AkkaHostedService never
registered LocalHandlerType.Integration). It was an early scaffold the
architecture routed around — the brokered External→Central→Site→Central
round-trip is served by the Inbound API's routed-site-script path (the
RouteTo* verbs, driven from CommunicationServiceInstanceRouter), which is
live, tested, and shares IntegrationTimeout.

Decision (#32): delete. Removed the IntegrationCall{Request,Response}
messages, RouteIntegrationCallAsync, the SiteCommunicationActor receive
block + _integrationHandler field + LocalHandlerType.Integration, and the
four tests that covered them (2 actor, 2 message-contract, 1 dispatcher-
reject, 1 mapper-reject). KEPT IntegrationTimeout — it is the live
timeout for the RouteTo* verbs. Updated the exclusion-narrative comments
(proto/mapper/dispatcher), design §4, the components doc timeout table,
and marked the known-issue RESOLVED.

Full solution build clean (0/0); Communication 634 + Host 421 green.
Net -172/+20 across 14 files. Not in the gRPC proto (was deliberately
excluded there), so no wire-format change.

docs/requirements/Component-Communication.md

@@ -46,6 +46,7 @@ Both central and site clusters. Each side has communication actors that handle m
 - Central routes the request to the appropriate site.
 - Site reads values from the Instance Actor and responds.
 - Central returns the response to the external system.
+- **Implementation**: this brokered round-trip is served by the **Inbound API's routed-site-script path** — a central-side inbound API method script composes the typed `RouteTo*` verbs on `CommunicationService` (`RouteToCall`, `RouteToGetAttributes`, `RouteToSetAttributes`, `RouteToWaitForAttribute`), driven from `InboundAPI/CommunicationServiceInstanceRouter` and sharing `IntegrationTimeout`. An earlier generic `IntegrationCallRequest` primitive was scaffolded for this pattern but never wired to a producer or a site handler; it was removed as dead code (Gitea #32, 2026-07-23).
 
 ### 5. Recipe/Command Delivery (External System → Central → Site)
 - **Pattern**: Fire-and-forget with acknowledgment.