feat(centralui): OffsetPager reusable pagination component (T35a)

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

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+@namespace ZB.MOM.WW.ScadaBridge.CentralUI.Components.Shared
+
+@* T35a — reusable offset-pagination bar.  Purely presentational: the host page
+   owns page-number state, query execution, and the HasNextPage decision.
+   Parameters: Page, PageChanged, HasNextPage, TotalCount, PageSize, Disabled. *@
+
+<div class="d-flex align-items-center gap-2">
+    <button class="btn btn-outline-secondary btn-sm"
+            data-test="pager-prev"
+            disabled="@(!HasPrev || Disabled)"
+            @onclick="OnPrevAsync">
+        Previous
+    </button>
+
+    <span data-test="pager-summary">@SummaryText</span>
+
+    <button class="btn btn-outline-secondary btn-sm"
+            data-test="pager-next"
+            disabled="@(!HasNextPage || Disabled)"
+            @onclick="OnNextAsync">
+        Next
+    </button>
+</div>
+
+@code {
+    [Parameter] public int Page { get; set; } = 1;
+    [Parameter] public EventCallback<int> PageChanged { get; set; }
+    [Parameter] public bool HasNextPage { get; set; }
+    [Parameter] public int? TotalCount { get; set; }
+    [Parameter] public int PageSize { get; set; }
+    [Parameter] public bool Disabled { get; set; }
+
+    private bool HasPrev => Page > 1;
+
+    private int? PageCount =>
+        TotalCount is { } t && PageSize > 0
+            ? (int)Math.Ceiling(t / (double)PageSize)
+            : (int?)null;
+
+    private string SummaryText
+    {
+        get
+        {
+            var text = $"Page {Page}";
+            if (PageCount is { } pc) text += $" of {pc}";
+            if (TotalCount is { } total) text += $" · {total} total";
+            return text;
+        }
+    }
+
+    private Task OnPrevAsync() => PageChanged.InvokeAsync(Page - 1);
+    private Task OnNextAsync() => PageChanged.InvokeAsync(Page + 1);
+}

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Shared/OffsetPagerTests.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>
+/// bUnit tests for the <see cref="OffsetPager"/> reusable pagination bar (T35a).
+/// The component is purely presentational — it emits <c>PageChanged</c> callbacks
+/// and renders disabled states; the host page owns page-number and query state.
+/// </summary>
+public class OffsetPagerTests : BunitContext
+{
+    // ── PrevDisabled_OnFirstPage ──────────────────────────────────────────────
+
+    [Fact]
+    public void PrevDisabled_OnFirstPage()
+    {
+        var cut = Render<OffsetPager>(ps => ps
+            .Add(p => p.Page, 1)
+            .Add(p => p.HasNextPage, true));
+
+        var prev = cut.Find("[data-test='pager-prev']");
+
+        Assert.NotNull(prev.GetAttribute("disabled"));
+    }
+
+    // ── NextDisabled_WhenNoNextPage ───────────────────────────────────────────
+
+    [Fact]
+    public void NextDisabled_WhenNoNextPage()
+    {
+        var cut = Render<OffsetPager>(ps => ps
+            .Add(p => p.Page, 3)
+            .Add(p => p.HasNextPage, false));
+
+        var next = cut.Find("[data-test='pager-next']");
+
+        Assert.NotNull(next.GetAttribute("disabled"));
+    }
+
+    // ── Next_Click_EmitsPagePlusOne ───────────────────────────────────────────
+
+    [Fact]
+    public void Next_Click_EmitsPagePlusOne()
+    {
+        int? emitted = null;
+        var cut = Render<OffsetPager>(ps => ps
+            .Add(p => p.Page, 2)
+            .Add(p => p.HasNextPage, true)
+            .Add(p => p.PageChanged,
+                EventCallback.Factory.Create<int>(this, v => emitted = v)));
+
+        cut.Find("[data-test='pager-next']").Click();
+
+        Assert.Equal(3, emitted);
+    }
+
+    // ── Prev_Click_EmitsPageMinusOne ─────────────────────────────────────────
+
+    [Fact]
+    public void Prev_Click_EmitsPageMinusOne()
+    {
+        int? emitted = null;
+        var cut = Render<OffsetPager>(ps => ps
+            .Add(p => p.Page, 2)
+            .Add(p => p.HasNextPage, false)
+            .Add(p => p.PageChanged,
+                EventCallback.Factory.Create<int>(this, v => emitted = v)));
+
+        cut.Find("[data-test='pager-prev']").Click();
+
+        Assert.Equal(1, emitted);
+    }
+
+    // ── Summary_RendersPageOfTotal ────────────────────────────────────────────
+
+    [Fact]
+    public void Summary_RendersPageOfTotal()
+    {
+        var cut = Render<OffsetPager>(ps => ps
+            .Add(p => p.Page, 2)
+            .Add(p => p.PageSize, 50)
+            .Add(p => p.TotalCount, 230)
+            .Add(p => p.HasNextPage, true));
+
+        var summary = cut.Find("[data-test='pager-summary']");
+
+        Assert.Contains("Page 2 of 5", summary.TextContent);
+        Assert.Contains("230 total", summary.TextContent);
+    }
+
+    // ── BothDisabled_WhenDisabled ─────────────────────────────────────────────
+
+    [Fact]
+    public void BothDisabled_WhenDisabled()
+    {
+        var cut = Render<OffsetPager>(ps => ps
+            .Add(p => p.Page, 3)
+            .Add(p => p.HasNextPage, true)
+            .Add(p => p.Disabled, true));
+
+        var prev = cut.Find("[data-test='pager-prev']");
+        var next = cut.Find("[data-test='pager-next']");
+
+        Assert.NotNull(prev.GetAttribute("disabled"));
+        Assert.NotNull(next.GetAttribute("disabled"));
+    }
+}