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/ui/Badge.svelte

@@ -10,7 +10,7 @@
   } = $props();
 
   const baseClass =
-    'inline-flex shrink-0 whitespace-nowrap rounded-full py-1 px-2.5 text-[0.6875rem] font-medium transition-all ring-1 no-underline focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-offset-1';
+    'inline-flex shrink-0 whitespace-nowrap rounded-full py-1 px-2.5 text-[0.6875rem] font-medium transition-colors ring-1 no-underline focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-offset-1';
 
   const variantClasses = $derived(
     {