docs(auditlog): generalize two stale XML-doc comments

- AddColumnIfMissing is now shared by ExecutionId and ParentExecutionId;
  drop the ExecutionId-specific tag.
- AuditLogRepository.GetExecutionTreeAsync doc no longer hardcodes the
  MAXRECURSION literal; reference the ExecutionChainMaxDepth const instead.

src/ScadaLink.AuditLog/Site/SqliteAuditWriter.cs

@@ -147,8 +147,9 @@ public class SqliteAuditWriter : IAuditWriter, ISiteAuditQueue, IAsyncDisposable
     }
 
     /// <summary>
-    /// Audit Log #23 (ExecutionId): adds a column to <c>AuditLog</c> only when
-    /// it is not already present. SQLite lacks <c>ADD COLUMN IF NOT EXISTS</c>,
+    /// Audit Log #23: additively adds a column to <c>AuditLog</c> only when
+    /// it is not already present (used for <c>ExecutionId</c> and
+    /// <c>ParentExecutionId</c>). SQLite lacks <c>ADD COLUMN IF NOT EXISTS</c>,
     /// so the schema is probed via <c>PRAGMA table_info</c> first. Idempotent —
     /// safe to run on every <see cref="InitializeSchema"/>. Mirrors
     /// <c>StoreAndForwardStorage.AddColumnIfMissingAsync</c>; kept synchronous