refactor(client): replace hardcoded API URLs with ApiRoutes constants

Centralizes all API endpoint strings in ApiRoutes for consistency and
easier maintenance. Adds Hubs class for SignalR endpoints. Removes
completed plan files.

NEW/src/JdeScoping.Core/ApiContracts/ApiRoutes.cs

@@ -192,4 +192,13 @@ public static class ApiRoutes
         /// <summary>Route to reload pipelines.</summary>
         public const string Reload = "api/pipelines/reload";
     }
+
+    /// <summary>
+    /// Routes for SignalR hub endpoints.
+    /// </summary>
+    public static class Hubs
+    {
+        /// <summary>Route for the status hub (real-time search updates).</summary>
+        public const string Status = "/hubs/status";
+    }
 }