feat(auditlog): thread ExecutionId through S&F for retry-loop cached rows

The store-and-forward retry loop emits the per-attempt and terminal cached
audit rows (ApiCallCached/DbWriteCached Attempted, CachedResolve) via
CachedCallLifecycleBridge from a CachedCallAttemptContext, not from the
script context. ExecutionId (and SourceScript) were not threaded through the
S&F buffer, so those rows had ExecutionId = null and SourceScript = null.

Thread both, additively, from the cached-call enqueue path:

- StoreAndForwardMessage gains ExecutionId (Guid?) / SourceScript (string?).
- StoreAndForwardStorage adds nullable execution_id / source_script columns
  via an idempotent PRAGMA-probed ALTER TABLE migration; rows persisted by
  an older build read back null (back-compat).
- StoreAndForwardService.EnqueueAsync gains optional executionId /
  sourceScript params, stamped onto the buffered message and surfaced on the
  CachedCallAttemptContext built in the retry loop.
- CachedCallAttemptContext gains ExecutionId / SourceScript.
- CachedCallLifecycleBridge.BuildPacket sets AuditEvent.ExecutionId and
  AuditEvent.SourceScript from the context (replacing the hard-coded
  SourceScript = null and its now-stale comment).
- IExternalSystemClient.CachedCallAsync / IDatabaseGateway.CachedWriteAsync
  gain optional executionId / sourceScript params; ScriptRuntimeContext's
  CachedCall / CachedWrite helpers pass _executionId / _sourceScript.

Script-side cached rows (CachedSubmit, immediate Attempted+Resolve) are
unchanged. All threading is additive — old buffered S&F rows still
deserialize and process with the new fields null.

src/ScadaLink.SiteRuntime/Scripts/ScriptRuntimeContext.cs

@@ -513,7 +513,12 @@ public class ScriptRuntimeContext
                     parameters,
                     _instanceName,
                     cancellationToken,
-                    trackedId).ConfigureAwait(false);
+                    trackedId,
+                    // Audit Log #23 (ExecutionId Task 4): thread the script
+                    // execution's ExecutionId + SourceScript so a buffered
+                    // cached call's retry-loop audit rows carry them.
+                    executionId: _executionId,
+                    sourceScript: _sourceScript).ConfigureAwait(false);
             }
             catch (Exception ex)
             {
@@ -1096,7 +1101,12 @@ public class ScriptRuntimeContext
             try
             {
                 await _gateway.CachedWriteAsync(
-                    name, sql, parameters, _instanceName, cancellationToken, trackedId)
+                    name, sql, parameters, _instanceName, cancellationToken, trackedId,
+                    // Audit Log #23 (ExecutionId Task 4): thread the script
+                    // execution's ExecutionId + SourceScript so a buffered
+                    // cached write's retry-loop audit rows carry them.
+                    executionId: _executionId,
+                    sourceScript: _sourceScript)
                     .ConfigureAwait(false);
             }
             catch (Exception ex)