feat(blocks): data-block PascalCase identifier on every CMS block

Adds data-block="PascalName" alongside existing data-block-type
snake_case so blocks can be located via [data-block="Calendar"] etc.
in DevTools. Snake-case attribute kept for backward compat.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/lib/components/blocks/QuoteCarouselBlock.svelte

@@ -68,7 +68,7 @@
 
 <div
   class="quote-carousel {layoutClasses}"
-  data-block-type="quote_carousel"
+  data-block="QuoteCarousel" data-block-type="quote_carousel"
   data-block-slug={block._slug}
   onmouseenter={() => (paused = true)}
   onmouseleave={() => (paused = false)}