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/Styleguide/DataInputSection.razor

@@ -120,6 +120,7 @@
 				<DCheckbox @bind-Value="check" disabled />
 			</div>
 			<DCheckbox @bind-Value="check" Color="DColor.Primary" LabelText="@($"Checked: {check}")" />
+			<DCheckbox @bind-Value="mixedCheck" @bind-Indeterminate="mixed" LabelText="@(mixed ? "Indeterminate (click to clear)" : $"Checked: {mixedCheck}")" />
 			<DCheckbox @bind-Value="model.Terms" LabelText="I accept the terms (must be checked)" />
 			<ValidationMessage For="() => model.Terms" class="text-error text-xs" />
 		</section>
@@ -333,6 +334,8 @@
 </EditForm>
 
 @code {
+	bool mixedCheck;
+	bool mixed = true;
 	class DemoModel
 	{
 		[Required] public string Name { get; set; }