feat(siteruntime): ExternalSystem.CachedCall emits CachedSubmit telemetry (#23 M3)

Rework ScriptRuntimeContext.ExternalSystem.CachedCall to fit the M3
combined-telemetry model:

* Mints a fresh TrackedOperationId and emits one CachedSubmit packet
  via ICachedCallTelemetryForwarder BEFORE handing the call off — the
  SiteCalls row is materialised before the first delivery attempt so
  Tracking.Status(id) can observe a Submitted row even if immediate
  delivery resolves before the helper returns.
* Threads the TrackedOperationId into IExternalSystemClient.CachedCallAsync
  as a new optional parameter (and into IDatabaseGateway.CachedWriteAsync
  for the Database mirror set up here for E6). The gateway uses the id
  as the StoreAndForward messageId so the retry loop (Tasks E4/E5) can
  recover it from StoreAndForwardMessage.Id.
* Returns the TrackedOperationId rather than ExternalCallResult — the
  script's contract is now "get a tracking handle, observe outcome via
  Tracking.Status". Best-effort emission: a thrown forwarder is logged
  + swallowed; the original call still runs and the id is still returned.

DatabaseHelper gets the matching siteId / sourceScript / forwarder
fields and a parallel CachedSubmit emitter (Channel=DbOutbound) so Task
E6's Database.CachedWrite mirror plugs in without further runtime
wiring.

New ICachedCallTelemetryForwarder seam in Commons.Interfaces.Services
so SiteRuntime depends on Commons (existing arrow) rather than
ScadaLink.AuditLog (would have introduced a new dependency).

Bundle E task E3 (and helper-shape work for E6).

src/ScadaLink.AuditLog/Site/Telemetry/CachedCallTelemetryForwarder.cs

@@ -45,7 +45,7 @@ namespace ScadaLink.AuditLog.Site.Telemetry;
 /// both M2 and M3 emissions.
 /// </para>
 /// </remarks>
-public sealed class CachedCallTelemetryForwarder
+public sealed class CachedCallTelemetryForwarder : ICachedCallTelemetryForwarder
 {
     private readonly IAuditWriter _auditWriter;
     private readonly IOperationTrackingStore _trackingStore;