fix(central-ui): never render DB connection strings on Integration Definitions list

Connection strings carry credentials; the Database Connections tab rendered the
full string (text + title tooltip) for any Design/Admin user. Replace with a
non-sensitive 'hidden — edit to view' hint so it never reaches the browser DOM.
Connection strings remain editable on the create/edit form. Adds a bUnit
regression guard asserting the seeded secret is absent from the rendered list.

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Design/ExternalSystems.razor

@@ -245,7 +245,8 @@
                                         </div>
                                     </div>
                                 </div>
-                                <p class="small text-muted text-truncate mb-1" title="@dc.ConnectionString">@dc.ConnectionString</p>
+                                @* Connection strings carry credentials — never rendered here (not even for admins). Shown only on the create/edit form. *@
+                                <p class="small text-muted fst-italic mb-1">Connection string hidden — edit to view</p>
                                 <div>
                                     <span class="badge bg-light text-dark me-1">Max @dc.MaxRetries retries</span>
                                     <span class="badge bg-light text-dark">Delay @dc.RetryDelay.TotalSeconds s</span>

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Design/ExternalSystemsConnectionStringHidingTests.cs

@@ -0,0 +1,73 @@
+using System.Security.Claims;
+using Bunit;
+using Microsoft.AspNetCore.Components.Authorization;
+using Microsoft.Extensions.DependencyInjection;
+using NSubstitute;
+using ZB.MOM.WW.ScadaBridge.CentralUI.Components.Shared;
+using ZB.MOM.WW.ScadaBridge.Commons.Entities.ExternalSystems;
+using ZB.MOM.WW.ScadaBridge.Commons.Entities.InboundApi;
+using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
+using ZB.MOM.WW.ScadaBridge.Security;
+using ExternalSystems = ZB.MOM.WW.ScadaBridge.CentralUI.Components.Pages.Design.ExternalSystems;
+
+namespace ZB.MOM.WW.ScadaBridge.CentralUI.Tests.Design;
+
+/// <summary>
+/// Security regression guard: the Integration Definitions list (Database Connections
+/// tab) must NEVER render a connection string — it carries credentials. Connection
+/// strings are shown only on the create/edit form. This test seeds a connection whose
+/// string contains a sentinel password and asserts it is absent from the rendered
+/// markup of the list (so it never reaches the browser DOM, even for an admin/designer).
+/// </summary>
+public class ExternalSystemsConnectionStringHidingTests : BunitContext
+{
+    private readonly IExternalSystemRepository _repo = Substitute.For<IExternalSystemRepository>();
+    private readonly IInboundApiRepository _inbound = Substitute.For<IInboundApiRepository>();
+    private readonly IDialogService _dialog = Substitute.For<IDialogService>();
+
+    public ExternalSystemsConnectionStringHidingTests()
+    {
+        Services.AddSingleton(_repo);
+        Services.AddSingleton(_inbound);
+        Services.AddSingleton(_dialog);
+
+        var claims = new[]
+        {
+            new Claim(JwtTokenService.UsernameClaimType, "tester"),
+            new Claim(JwtTokenService.RoleClaimType, "Designer"),
+        };
+        var user = new ClaimsPrincipal(new ClaimsIdentity(claims, "TestAuth"));
+        Services.AddSingleton<AuthenticationStateProvider>(new TestAuthStateProvider(user));
+        Services.AddAuthorizationCore();
+        AuthorizationPolicies.AddScadaBridgeAuthorization(Services);
+    }
+
+    [Fact]
+    public void DbConnectionsTab_DoesNotRenderConnectionString()
+    {
+        const string secret = "Server=db.internal;User Id=sa;Password=SuperSecret#123;";
+
+        _repo.GetAllExternalSystemsAsync(Arg.Any<CancellationToken>())
+            .Returns((IReadOnlyList<ExternalSystemDefinition>)new List<ExternalSystemDefinition>());
+        _repo.GetAllDatabaseConnectionsAsync(Arg.Any<CancellationToken>())
+            .Returns((IReadOnlyList<DatabaseConnectionDefinition>)new List<DatabaseConnectionDefinition>
+            {
+                new("AppDb", secret) { Id = 1 },
+            });
+        _inbound.GetAllApiMethodsAsync(Arg.Any<CancellationToken>())
+            .Returns((IReadOnlyList<ApiMethod>)new List<ApiMethod>());
+
+        var cut = Render<ExternalSystems>();
+
+        // Wait for the async load to complete (tabs render only once _loading == false),
+        // then activate the Database Connections tab so its cards render.
+        cut.WaitForAssertion(() =>
+            Assert.Contains(cut.FindAll("button.nav-link"), b => b.TextContent.Contains("Database Connections")));
+        cut.FindAll("button.nav-link").First(b => b.TextContent.Contains("Database Connections")).Click();
+        cut.WaitForAssertion(() => Assert.Contains("AppDb", cut.Markup));
+
+        // The card renders (name visible) but the credential-bearing connection string must not.
+        Assert.DoesNotContain(secret, cut.Markup);
+        Assert.DoesNotContain("SuperSecret#123", cut.Markup);
+    }
+}