feat(centralui): KeysetPager reusable cursor-pagination component (T35b)

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Shared/KeysetPager.razor

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+@* Reusable keyset (cursor) pagination button bar — purely presentational.
+   All cursor/navigation logic lives in the consuming page via callbacks. *@
+
+<div class="d-flex align-items-center gap-2">
+    <button class="btn btn-outline-secondary btn-sm"
+            data-test="keyset-prev"
+            disabled="@(!CanGoBack || Disabled)"
+            @onclick="OnPrevious">Previous</button>
+    <span data-test="keyset-summary">Page @PageNumber · @RowCount rows</span>
+    <button class="btn btn-outline-secondary btn-sm"
+            data-test="keyset-next"
+            disabled="@(!HasNextPage || Disabled)"
+            @onclick="OnNext">Next</button>
+</div>
+
+@code {
+    [Parameter] public int PageNumber { get; set; } = 1;
+    [Parameter] public int RowCount { get; set; }
+    [Parameter] public bool CanGoBack { get; set; }
+    [Parameter] public bool HasNextPage { get; set; }
+    [Parameter] public bool Disabled { get; set; }
+    [Parameter] public EventCallback OnPrevious { get; set; }
+    [Parameter] public EventCallback OnNext { get; set; }
+}

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

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+using Bunit;
+using Microsoft.AspNetCore.Components;
+using ZB.MOM.WW.ScadaBridge.CentralUI.Components.Shared;
+
+namespace ZB.MOM.WW.ScadaBridge.CentralUI.Tests.Shared;
+
+/// <summary>
+/// Component tests for <see cref="KeysetPager"/> — the purely-presentational
+/// cursor-pagination button bar shared by SiteCallsReport and AuditResultsGrid.
+/// </summary>
+public class KeysetPagerTests : BunitContext
+{
+    [Fact]
+    public void PrevDisabled_WhenCannotGoBack()
+    {
+        var cut = Render<KeysetPager>(ps => ps
+            .Add(p => p.CanGoBack, false)
+            .Add(p => p.HasNextPage, true));
+
+        var prev = cut.Find("[data-test='keyset-prev']");
+
+        Assert.NotNull(prev.GetAttribute("disabled"));
+    }
+
+    [Fact]
+    public void NextDisabled_WhenNoNextPage()
+    {
+        var cut = Render<KeysetPager>(ps => ps
+            .Add(p => p.CanGoBack, true)
+            .Add(p => p.HasNextPage, false));
+
+        var next = cut.Find("[data-test='keyset-next']");
+
+        Assert.NotNull(next.GetAttribute("disabled"));
+    }
+
+    [Fact]
+    public void Prev_Click_InvokesOnPrevious()
+    {
+        var fired = false;
+        var cut = Render<KeysetPager>(ps => ps
+            .Add(p => p.CanGoBack, true)
+            .Add(p => p.HasNextPage, false)
+            .Add(p => p.OnPrevious,
+                EventCallback.Factory.Create(this, () => { fired = true; })));
+
+        cut.Find("[data-test='keyset-prev']").Click();
+
+        Assert.True(fired);
+    }
+
+    [Fact]
+    public void Next_Click_InvokesOnNext()
+    {
+        var fired = false;
+        var cut = Render<KeysetPager>(ps => ps
+            .Add(p => p.CanGoBack, false)
+            .Add(p => p.HasNextPage, true)
+            .Add(p => p.OnNext,
+                EventCallback.Factory.Create(this, () => { fired = true; })));
+
+        cut.Find("[data-test='keyset-next']").Click();
+
+        Assert.True(fired);
+    }
+
+    [Fact]
+    public void Summary_RendersPageAndRows()
+    {
+        var cut = Render<KeysetPager>(ps => ps
+            .Add(p => p.PageNumber, 3)
+            .Add(p => p.RowCount, 42));
+
+        var summary = cut.Find("[data-test='keyset-summary']");
+
+        Assert.Contains("Page 3", summary.TextContent);
+        Assert.Contains("42 rows", summary.TextContent);
+    }
+
+    [Fact]
+    public void BothDisabled_WhenDisabled()
+    {
+        var cut = Render<KeysetPager>(ps => ps
+            .Add(p => p.CanGoBack, true)
+            .Add(p => p.HasNextPage, true)
+            .Add(p => p.Disabled, true));
+
+        var prev = cut.Find("[data-test='keyset-prev']");
+        var next = cut.Find("[data-test='keyset-next']");
+
+        Assert.NotNull(prev.GetAttribute("disabled"));
+        Assert.NotNull(next.GetAttribute("disabled"));
+    }
+}