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.Commons/Interfaces/Services/ICachedCallLifecycleObserver.cs

@@ -71,6 +71,16 @@ public interface ICachedCallLifecycleObserver
 /// rows carry the same <c>SourceScript</c> provenance the script-side cached
 /// rows already do. <c>null</c> when not known.
 /// </param>
+/// <param name="ParentExecutionId">
+/// Audit Log #23 (ParentExecutionId Task 6): the <c>ExecutionId</c> of the
+/// inbound-API request that spawned the originating script execution,
+/// threaded through the store-and-forward buffer alongside
+/// <paramref name="ExecutionId"/>. The audit bridge stamps it onto the
+/// retry-loop <c>ApiCallCached</c>/<c>DbWriteCached</c> Attempted and
+/// <c>CachedResolve</c> rows so they correlate back to the spawning run.
+/// <c>null</c> for a non-routed run and for rows buffered before Task 6
+/// (back-compat).
+/// </param>
 public sealed record CachedCallAttemptContext(
     TrackedOperationId TrackedOperationId,
     string Channel,
@@ -85,7 +95,8 @@ public sealed record CachedCallAttemptContext(
     int? DurationMs,
     string? SourceInstanceId,
     Guid? ExecutionId = null,
-    string? SourceScript = null);
+    string? SourceScript = null,
+    Guid? ParentExecutionId = null);
 
 /// <summary>
 /// Coarse outcome of one cached-call delivery attempt, observed from inside

src/ScadaLink.Commons/Interfaces/Services/IDatabaseGateway.cs

@@ -40,6 +40,14 @@ public interface IDatabaseGateway
     /// threaded onto the buffered S&F message alongside
     /// <paramref name="executionId"/>. <c>null</c> when not known.
     /// </param>
+    /// <param name="parentExecutionId">
+    /// Audit Log #23 (ParentExecutionId Task 6): the <c>ExecutionId</c> of the
+    /// inbound-API request that spawned the originating script execution.
+    /// When the write is buffered on a transient failure this is threaded onto
+    /// the S&amp;F message alongside <paramref name="executionId"/> so the
+    /// retry-loop cached-write audit rows carry it. <c>null</c> for a
+    /// non-routed run.
+    /// </param>
     Task CachedWriteAsync(
         string connectionName,
         string sql,
@@ -48,5 +56,6 @@ public interface IDatabaseGateway
         CancellationToken cancellationToken = default,
         TrackedOperationId? trackedOperationId = null,
         Guid? executionId = null,
-        string? sourceScript = null);
+        string? sourceScript = null,
+        Guid? parentExecutionId = null);
 }

src/ScadaLink.Commons/Interfaces/Services/IExternalSystemClient.cs

@@ -41,6 +41,14 @@ public interface IExternalSystemClient
     /// threaded onto the buffered S&F message alongside
     /// <paramref name="executionId"/>. <c>null</c> when not known.
     /// </param>
+    /// <param name="parentExecutionId">
+    /// Audit Log #23 (ParentExecutionId Task 6): the <c>ExecutionId</c> of the
+    /// inbound-API request that spawned the originating script execution.
+    /// When the call is buffered on a transient failure this is threaded onto
+    /// the S&amp;F message alongside <paramref name="executionId"/> so the
+    /// retry-loop cached-call audit rows carry it. <c>null</c> for a non-routed
+    /// run.
+    /// </param>
     Task<ExternalCallResult> CachedCallAsync(
         string systemName,
         string methodName,
@@ -49,7 +57,8 @@ public interface IExternalSystemClient
         CancellationToken cancellationToken = default,
         TrackedOperationId? trackedOperationId = null,
         Guid? executionId = null,
-        string? sourceScript = null);
+        string? sourceScript = null,
+        Guid? parentExecutionId = null);
 }
 
 /// <summary>