feat(posts): search, upcoming events, RSS feed

- Client-side search on /posts/ (full archive, ~2-char threshold)
- Upcoming-events block at top of /posts/ from isEvent+eventDate posts
- RSS feed at /posts/rss.xml via @astrojs/rss
- Layout head: rss autodiscovery link
- RSS subscribe link below the listing
- Style tweaks on QuoteBlock and PostOverviewBlock

src/components/blocks/PostOverviewBlock.svelte

@@ -59,8 +59,8 @@
   {/if}
 
   {#if posts.length > 0}
-    <div class="mt-3 text-sm">
-      <a href="/posts/" class="inline-flex items-center gap-1 text-zinc-700 hover:text-zinc-900 hover:underline">
+    <div class="mt-3 text-xs px-2">
+      <a href="/posts/" class="inline-flex items-center gap-1 text-zinc-700 hover:text-zinc-900 hover:underline !no-underline">
         {t(T.post_overview_all)}
         <span aria-hidden="true">→</span>
       </a>

src/components/blocks/QuoteBlock.svelte

@@ -9,10 +9,10 @@
 </script>
 
 <div class={layoutClasses} data-block-type="quote" data-block-slug={block._slug}>
-  <blockquote class="border-l-4 border-wald-700 pl-4 {variantClass}">
-    <p class="text-xl font-semibold text-wald-700">{block.quote ?? ""}</p>
+  <blockquote class="border-l-2 border-wald-400 pl-4 {variantClass}">
+    <p class="text-lg font-extralight text-wald-600">{block.quote ?? ""}</p>
     {#if block.author}
-      <cite class="mt-1 block not-italic text-sm text-wald-300">{block.author}</cite>
+      <cite class="block font-sans! text-xs text-wald-400"> » {block.author}</cite>
       {/if}
     </blockquote>
 </div>