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.

src/ZB.MOM.WW.ScadaBridge.Communication/CommunicationService.cs

@@ -224,21 +224,13 @@ public class CommunicationService
     }
 
     // ── Pattern 4: Integration Routing ──
-
-    /// <summary>
-    /// Routes an integration call to a site.
-    /// </summary>
-    /// <param name="siteId">The target site identifier.</param>
-    /// <param name="request">The integration call request.</param>
-    /// <param name="cancellationToken">Cancellation token.</param>
-    /// <returns>The integration call response.</returns>
-    public async Task<IntegrationCallResponse> RouteIntegrationCallAsync(
-        string siteId, IntegrationCallRequest request, CancellationToken cancellationToken = default)
-    {
-        var envelope = new SiteEnvelope(siteId, request);
-        return await GetActor().Ask<IntegrationCallResponse>(
-            envelope, _options.IntegrationTimeout, cancellationToken);
-    }
+    // The brokered "External System → Central → Site → Central → External System"
+    // round-trip (design §4) is served by the Inbound API's routed-site-script
+    // path — the RouteTo* verbs below (RouteToCall / RouteToGetAttributes /
+    // RouteToSetAttributes / RouteToWaitForAttribute), driven from
+    // InboundAPI/CommunicationServiceInstanceRouter and sharing IntegrationTimeout.
+    // The earlier generic IntegrationCallRequest primitive was never wired to a
+    // producer or a site handler and was removed as dead code (Gitea #32).
 
     // ── Pattern 5: Debug View ──