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/Accordion.svelte

@@ -32,7 +32,7 @@
   }
 </script>
 
-<details {id} {open} ontoggle={onToggle} class="pt-4 border-t border-zinc-200 group {cls}">
+<details {id} {open} ontoggle={onToggle} class="pt-4 border-t border-stein-200 group {cls}">
   <summary class="flex cursor-pointer list-none items-center gap-2 text-sm font-medium select-none">
     <Icon icon="mdi:chevron-right" class="size-4 shrink-0 transition-transform group-open:rotate-90" />
     {label}