feat(ui): add primary/backup endpoint fields to data connection form

src/ScadaLink.CentralUI/Components/Pages/Admin/DataConnections.razor

@@ -32,7 +32,8 @@
                     <th>Name</th>
                     <th>Protocol</th>
                     <th>Site</th>
-                    <th>Configuration</th>
+                    <th>Primary Config</th>
+                    <th>Backup Config</th>
                     <th style="width: 160px;">Actions</th>
                 </tr>
             </thead>
@@ -40,7 +41,7 @@
                 @if (_connections.Count == 0)
                 {
                     <tr>
-                        <td colspan="6" class="text-muted text-center">No data connections configured.</td>
+                        <td colspan="7" class="text-muted text-center">No data connections configured.</td>
                     </tr>
                 }
                 @foreach (var conn in _connections)
@@ -51,6 +52,7 @@
                         <td><span class="badge bg-secondary">@conn.Protocol</span></td>
                         <td>@(_siteLookup.GetValueOrDefault(conn.SiteId)?.Name ?? $"Site {conn.SiteId}")</td>
                         <td class="text-muted small text-truncate" style="max-width: 300px;">@(conn.PrimaryConfiguration ?? "—")</td>
+                        <td class="text-muted small text-truncate" style="max-width: 300px;">@(conn.BackupConfiguration ?? "—")</td>
                         <td>
                             <button class="btn btn-outline-primary btn-sm py-0 px-1 me-1"
                                     @onclick='() => NavigationManager.NavigateTo($"/admin/data-connections/{conn.Id}/edit")'>Edit</button>