site: layout width tiers + masonry glide — column changes animate instead of snapping

Named width tiers (mobile/narrow/regular/wide) with body max-width easing
between them; grid pages opt in via BaseLayout `wide`. Masonry is now
absolute-positioned with FLIP glides on column-count changes: targets are
computed from the *final* container width (reading --max, which flips
instantly while max-width tweens), mid-glide column changes retarget
instead of being dropped, and container height eases so content below
rides along.

Claude-Session: https://claude.ai/code/session_01ADR9r5rw5NuvvnCxfYbMuc

src/pages/index.astro

@@ -93,6 +93,7 @@ const itemList = buildItemList(
   lastUpdated={lastUpdated}
   ogImage={ogImage}
   jsonLd={[WEBSITE, ORGANIZATION, itemList]}
+  wide
 >
   {hero && hero.kind === 'review' && (
     <a href={hero.href} class="hero">