Harden topology editor save/discover flow and edge editing.

Guard unsaved changes, cancel discovery, block invalid links, preserve discovered_at on PUT, and normalize interface names for discovery keys.

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/services/api.ts

@@ -572,6 +572,7 @@ export const putTopologyGraph = (
       stroke_color?: string;
       stroke_width?: number;
       line_style?: string;
+      discovered_at?: string | null;
     }>;
   },
 ) => apiPut<TopologyGraph>(`/v1/topology/maps/${encodeURIComponent(mapId)}/graph`, body);