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/Badge.svelte

@@ -11,7 +11,7 @@
     switch (c) {
       case "green": return "bg-wald-50 text-wald-700 border border-wald-200";
       case "blue":  return "bg-himmel-50 text-himmel-700 border border-himmel-200";
-      case "amber": return "bg-[#fdf8ec] text-[#a6780a] border border-[#f0d98a]";
+      case "amber": return "bg-erde-50 text-erde-700 border border-erde-200";
       default:      return "bg-stein-100 text-stein-600 border border-stein-200";
     }
   }