Add carousel navigation and the mixed checkbox state, without script

These were left out because daisyUI does them with scripts or with links that
<base href="/"> breaks.

DCarousel:
- ShowNavigation adds previous/next links on each slide, and ShowIndicators adds
  a row of numbered links under the strip.
- The links point at the slides' ids under the current path, so Blazor treats
  them as same-page fragments and scrolls the strip.

DCheckbox:
- Indeterminate renders aria-checked="mixed", which daisyUI draws like
  :indeterminate.
- A click clears it through IndeterminateChanged.
- The neo inset well leaves the mixed state alone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Components/Daisy/DataDisplay/DCarouselItem.razor

@@ -1,10 +1,28 @@
 @inherits DComponentBase
+@implements IDisposable
 
-@* One slide of a DCarousel. *@
-<div @attributes="AdditionalAttributes" class="@Cx("carousel-item", Class)">
+@* One slide of a DCarousel. It registers with the carousel for its id and, with ShowNavigation, draws the
+   previous/next links over itself. *@
+<div @attributes="AdditionalAttributes" id="@Id" class="@Cx("carousel-item", HasNavigation ? "relative" : null, Class)">
 	@ChildContent
+	@if (HasNavigation)
+	{
+		<div class="absolute inset-x-2 top-1/2 flex -translate-y-1/2 justify-between">
+			<a href="@Parent.Link(Index - 1)" class="btn btn-circle btn-sm" aria-label="@Parent.PreviousText">❮</a>
+			<a href="@Parent.Link(Index + 1)" class="btn btn-circle btn-sm" aria-label="@Parent.NextText">❯</a>
+		</div>
+	}
 </div>
 
 @code {
+	[CascadingParameter] DCarousel Parent { get; set; }
 	[Parameter] public RenderFragment ChildContent { get; set; }
+
+	int Index => Parent?.IndexOf(this) ?? -1;
+	string Id => Parent is null ? null : Parent.SlideId(Index);
+	bool HasNavigation => Parent is { ShowNavigation: true, Count: > 1 };
+
+	protected override void OnInitialized() => Parent?.Add(this);
+
+	public void Dispose() => Parent?.Remove(this);
 }