refactor(ui): unify semantic presentation and table hierarchy

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Shared/DataTablePagerTests.cs

@@ -23,6 +23,39 @@ public class DataTablePagerTests : BunitContext
             .Add(p => p.RowContent, (RenderFragment<int>)(item => b => b.AddMarkupContent(0, $"<tr><td>{item}</td></tr>"))));
     }
 
+    /// <summary>True empty results show no contradictory one-to-zero range.</summary>
+    [Fact]
+    public void EmptyTable_ShowsZeroItems()
+    {
+        var cut = RenderTable(0);
+        Assert.Equal("0 items", cut.Find(".text-muted.small").TextContent.Trim());
+    }
+
+    /// <summary>Filtering to zero and clearing preserves the correct range and paging state.</summary>
+    [Fact]
+    public void FilterToEmpty_ThenClear_RestoresRealCount()
+    {
+        var cut = RenderTable(60);
+        cut.Render(p => p.Add(c => c.ShowSearch, true).Add(c => c.SearchFilter, (item, search) => item.ToString().Contains(search)));
+        cut.Find("input").Input("no-match");
+        Assert.Equal("0 items", cut.Find(".text-muted.small").TextContent.Trim());
+        cut.Find("button[aria-label='Clear search']").Click();
+        Assert.Contains("1–25 of 60 items", cut.Find(".text-muted.small").TextContent);
+    }
+
+    /// <summary>The reusable table has one named keyboard-accessible overflow region.</summary>
+    [Fact]
+    public void Table_HasNamedKeyboardScrollRegion()
+    {
+        var cut = RenderTable(4);
+        var region = cut.Find("[role=region]");
+        Assert.Equal("Data table", region.GetAttribute("aria-label"));
+        Assert.Equal("0", region.GetAttribute("tabindex"));
+        Assert.Single(region.QuerySelectorAll("table"));
+        cut.Render(p => p.Add(c => c.TableLabel, "Synthetic records"));
+        Assert.Equal("Synthetic records", cut.Find("[role=region]").GetAttribute("aria-label"));
+    }
+
     private static int NumberedPageButtons(IRenderedComponent<DataTable<int>> cut)
         => cut.FindAll("ul.pagination li.page-item button")
               .Count(b => int.TryParse(b.TextContent.Trim(), out _));

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/TopologyPageTests.cs

@@ -150,6 +150,26 @@ public class TopologyPageTests : BunitContext
             });
     }
 
+    /// <summary>Every load state keeps one semantic page title.</summary>
+    [Theory]
+    [InlineData("loading")]
+    [InlineData("loaded")]
+    [InlineData("error")]
+    public async Task PageTitle_RemainsOneH1AcrossLoadStates(string state)
+    {
+        SeedRepos();
+        var pending = new TaskCompletionSource<IReadOnlyList<Site>>(TaskCreationOptions.RunContinuationsAsynchronously);
+        if (state == "loading") _siteRepo.GetAllSitesAsync().Returns(pending.Task);
+        if (state == "error") _siteRepo.GetAllSitesAsync().Returns(Task.FromException<IReadOnlyList<Site>>(new Exception("local failure")));
+        var cut = Render<TopologyPage>();
+        try
+        {
+            Assert.Single(cut.FindAll("h1"));
+            Assert.Equal("Topology", cut.Find("h1").TextContent.Trim());
+        }
+        finally { await cut.InvokeAsync(() => pending.TrySetResult([])); }
+    }
+
     private IRenderedComponent<TopologyPage> RenderLoadedTopology()
     {
         var cut = Render<TopologyPage>();