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.Client/Services/AuthService.cs

@@ -1,5 +1,6 @@
 using System.Net.Http.Json;
 using JdeScoping.Client.Auth;
+using JdeScoping.Core.ApiContracts;
 using JdeScoping.Core.Models.Auth;
 
 namespace JdeScoping.Client.Services;
@@ -43,7 +44,7 @@ public class AuthService : IAuthService
             var request = new EncryptedLoginRequest(encryptedData);
 
             // Send encrypted request
-            var response = await _httpClient.PostAsJsonAsync("api/auth/login", request);
+            var response = await _httpClient.PostAsJsonAsync(ApiRoutes.Auth.Login, request);
 
             var result = await response.Content.ReadFromJsonAsync<LoginResultModel>();
             if (result is null)
@@ -72,7 +73,7 @@ public class AuthService : IAuthService
     {
         try
         {
-            await _httpClient.PostAsync("api/auth/logout", null);
+            await _httpClient.PostAsync(ApiRoutes.Auth.Logout, null);
         }
         catch
         {