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.AuditLog/Site/Telemetry/CachedCallLifecycleBridge.cs

@@ -137,6 +137,12 @@ public sealed class CachedCallLifecycleBridge : ICachedCallLifecycleObserver
                 // execution's per-run correlation id, threaded through the S&F
                 // buffer; null on rows buffered before Task 4 (back-compat).
                 ExecutionId = context.ExecutionId,
+                // Audit Log #23 (ParentExecutionId Task 6): the spawning
+                // inbound-API request's ExecutionId, threaded through the S&F
+                // buffer alongside ExecutionId so the retry-loop cached rows
+                // correlate back to the cross-execution chain. Null for a
+                // non-routed run and on rows buffered before Task 6.
+                ParentExecutionId = context.ParentExecutionId,
                 SourceSiteId = string.IsNullOrEmpty(context.SourceSite) ? null : context.SourceSite,
                 SourceInstanceId = context.SourceInstanceId,
                 // Audit Log #23 (ExecutionId Task 4): SourceScript is now