fix: derive work item ParentId from Hierarchy-Reverse relation

System.Parent field is not consistently populated by the Azure DevOps REST API,
causing parentId to come back null even when the work item has a parent.
Read the parent ID from the System.LinkTypes.Hierarchy-Reverse relation URL,
keeping the System.Parent field read as a fallback.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: viamus

src/Viamus.Azure.Devops.Mcp.Server/Services/AzureDevOpsService.cs

@@ -366,7 +366,15 @@ private static WorkItemDto MapToDto(WorkItem workItem, bool includeAllFields = f
 
             foreach (var relation in workItem.Relations)
             {
-                if (relation.Rel == "ArtifactLink" && !string.IsNullOrEmpty(relation.Url))
+                if (relation.Rel == "System.LinkTypes.Hierarchy-Reverse" && !string.IsNullOrEmpty(relation.Url))
+                {
+                    var lastSlash = relation.Url.LastIndexOf('/');
+                    if (lastSlash >= 0 && int.TryParse(relation.Url[(lastSlash + 1)..], out var parentIdFromRelation))
+                    {
+                        dto = dto with { ParentId = parentIdFromRelation };
+                    }
+                }
+                else if (relation.Rel == "ArtifactLink" && !string.IsNullOrEmpty(relation.Url))
                 {
                     // Commit URL format: vstfs:///Git/Commit/{projectId}%2F{repoId}%2F{commitId}
                     // Pull Request URL format: vstfs:///Git/PullRequestId/{projectId}%2F{repoId}%2F{prId}