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

Styles/neo.css

@@ -191,7 +191,7 @@
 
 /* Selectors: an inset well while unchecked; once checked they keep daisyUI's filled look. */
 @utility checkbox {
-	&:not(:where(:checked, :indeterminate, [aria-checked="true"], :disabled)) {
+	&:not(:where(:checked, :indeterminate, [aria-checked="true"], [aria-checked="mixed"], :disabled)) {
 		border-color: transparent;
 		background-image: linear-gradient(145deg, var(--neo-grad-dark), var(--neo-grad-light));
 		box-shadow: inset 2px 2px 4px var(--neo-dark), inset -2px -2px 4px var(--neo-light);