style(design): consistency sweep + UX upgrades

- Palette: gray/zinc/slate/neutral → stein, red → fire, amber → erde,
  sky → himmel, green → wald
- Footer: replaced raw rgb with stein tokens
- Radius: unified to rounded-xs across cards, buttons, inputs, pagination
- Buttons: .btn-primary/.btn-secondary now font-medium; added secondary
- Card hover: -translate-y-0.5 + shadow + wald-300 border
- Header active link: wald border-bottom + wald-700 text
- Mobile nav: bigger touch targets + wald active accent
- Pagination: prev/next text labels + wald-500 active state with
  separated shape/color classes to avoid Tailwind conflicts
- Lead paragraph: scoped .markdown > p:first-child for top-level
  MarkdownBlock only via [data-block-type="markdown"]
- Section dividers: subtle wald-200 gradient between content rows
- Global focus-visible ring (wald-500)
- Inline hex → palette tokens (Badge amber, Tag custom-color contrast)
- Font weights snapped to design system (300/400/500/600/700)
- transition-all → transition-colors where only color changes
- Removed em-dashes from user-visible templates

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

src/lib/components/PostCard.svelte

@@ -59,7 +59,7 @@
   layout="post"
   class={isPastEvent ? "opacity-70 grayscale" : ""}
 >
-  <div class="relative aspect-3/2 w-full overflow-hidden bg-gray-100">
+  <div class="relative aspect-3/2 w-full overflow-hidden bg-stein-100">
     {#if rawImg}
       <RustyImage
         src={rawImg}
@@ -79,7 +79,7 @@
         loading="lazy"
       />
     {:else}
-      <div class="w-full h-full flex items-center justify-center text-gray-300">
+      <div class="w-full h-full flex items-center justify-center text-stein-300">
         <svg xmlns="http://www.w3.org/2000/svg" class="size-12" viewBox="0 0 24 24" fill="currentColor" aria-hidden="true">
           <path d="M21 19V5c0-1.1-.9-2-2-2H5c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h14c1.1 0 2-.9 2-2zM8.5 13.5l2.5 3.01L14.5 12l4.5 6H5l3.5-4.5z"/>
         </svg>
@@ -92,7 +92,7 @@
     {/if}
     {#if isPastEvent}
       <div class="absolute top-2 right-2">
-        <span class="inline-flex items-center gap-1 rounded-full bg-neutral-800/90 px-2.5 py-1 text-[.65rem] font-semibold uppercase tracking-wide text-white shadow-sm">
+        <span class="inline-flex items-center gap-1 rounded-full bg-stein-800/90 px-2.5 py-1 text-[.65rem] font-semibold uppercase tracking-wide text-white shadow-sm">
           Vergangen
         </span>
       </div>
@@ -100,7 +100,7 @@
     {#if commentCount != null}
       <div class="absolute top-2 left-2">
         <span
-          class="inline-flex items-center gap-1 rounded-full bg-white/90 px-2 py-1 text-[.65rem] font-semibold tabular-nums text-zinc-700 shadow-sm"
+          class="inline-flex items-center gap-1 rounded-full bg-white/90 px-2 py-1 text-[.65rem] font-semibold tabular-nums text-stein-700 shadow-sm"
           aria-label={t(T.comments_count_aria, { count: commentCount })}
           title={t(T.comments_count_aria, { count: commentCount })}
         >