feat(auditlog): thread ParentExecutionId 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. The ExecutionId rollout (Task 4) already threaded ExecutionId
and SourceScript through this path; ParentExecutionId — the spawning
inbound-API request's ExecutionId — was not, so those retry-loop rows had
ParentExecutionId = null even for an inbound-API-routed run.

Thread it additively as a sibling at every carry point ExecutionId passes
through:

- StoreAndForwardMessage gains ParentExecutionId (Guid?).
- StoreAndForwardStorage adds a nullable parent_execution_id column via the
  same idempotent PRAGMA-probed ALTER TABLE migration; rows persisted by an
  older build read back null (back-compat). The defensive Guid.TryParse read
  helper (ParseExecutionId) is renamed ParseGuidColumn and reused for both
  columns so a corrupt value cannot abort the retry sweep.
- StoreAndForwardService.EnqueueAsync gains an optional parentExecutionId
  param, stamped onto the buffered message and surfaced on the
  CachedCallAttemptContext built in the retry loop.
- CachedCallAttemptContext gains ParentExecutionId.
- CachedCallLifecycleBridge.BuildPacket sets AuditEvent.ParentExecutionId
  from the context, beside the existing ExecutionId.
- IExternalSystemClient.CachedCallAsync / IDatabaseGateway.CachedWriteAsync
  gain an optional parentExecutionId param; ScriptRuntimeContext's CachedCall
  / CachedWrite helpers pass _parentExecutionId.

All threading is additive — ParentExecutionId is Guid? everywhere, null for
non-routed runs, and old buffered S&F rows still deserialize with the new
field null.

src/ScadaLink.SiteRuntime/Scripts/ScriptRuntimeContext.cs

@@ -564,7 +564,12 @@ public class ScriptRuntimeContext
                     // execution's ExecutionId + SourceScript so a buffered
                     // cached call's retry-loop audit rows carry them.
                     executionId: _executionId,
-                    sourceScript: _sourceScript).ConfigureAwait(false);
+                    sourceScript: _sourceScript,
+                    // Audit Log #23 (ParentExecutionId Task 6): thread the
+                    // spawning inbound-API request's ExecutionId so a buffered
+                    // cached call's retry-loop audit rows carry it too. Null
+                    // for a non-routed run.
+                    parentExecutionId: _parentExecutionId).ConfigureAwait(false);
             }
             catch (Exception ex)
             {
@@ -1178,7 +1183,12 @@ public class ScriptRuntimeContext
                     // execution's ExecutionId + SourceScript so a buffered
                     // cached write's retry-loop audit rows carry them.
                     executionId: _executionId,
-                    sourceScript: _sourceScript)
+                    sourceScript: _sourceScript,
+                    // Audit Log #23 (ParentExecutionId Task 6): thread the
+                    // spawning inbound-API request's ExecutionId so a buffered
+                    // cached write's retry-loop audit rows carry it too. Null
+                    // for a non-routed run.
+                    parentExecutionId: _parentExecutionId)
                     .ConfigureAwait(false);
             }
             catch (Exception ex)