feat(graph): add parent field to GraphNode domain entity

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/modules/graph/domain/entities.py

@@ -8,6 +8,7 @@ class GraphNode:
     label: str
     status: str         # FileStatus or "unknown"
     group_id: str
+    parent: str | None = None
 
 
 @dataclass

backend/tests/test_graph_service.py

@@ -80,3 +80,9 @@ def test_neighbors_unknown_node(graph_service, scan_result):
     neighbors = graph_service.get_neighbors(view, "NONEXISTENT")
     assert len(neighbors.nodes) == 0
     assert len(neighbors.edges) == 0
+
+
+def test_graph_node_has_parent_field(graph_service, scan_result):
+    view = graph_service.build_panorama(scan_result)
+    for node in view.nodes:
+        assert hasattr(node, 'parent')