feat: plakat redesign phase 1 (tokens, fonts, poster hero, header) (#74)

- New design tokens: signal red, ink and paper as RGB channels; ink and paper
  swap roles in dark mode so every component inverts cleanly
- Fonts via next/font: Bricolage Grotesque (with wdth/opsz axes), Geist,
  Geist Mono; drop Inter and Playfair
- Poster hero: kicker, giant DK0 wordmark that reacts to pointer distance
  (weight and width through a damped spring, desktop only, off for reduced
  motion), claim as h1, intro with thesis countdown, marquee strip
- Header in poster style: transparent over the red hero, paper strip with
  ink rule when scrolled or on subpages; drawer menu restyled
- Remove wavy SVG separators, CSS shader gradient, background blobs and
  unused providers that caused the pink/purple bands between sections
- Drop the global p/span/div color override so colors inherit properly
- New hero texts in de/en, tests and i18n key check updated

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/components/ThemeToggle.tsx

@@ -13,7 +13,7 @@ export function ThemeToggle() {
   }, []);
 
   if (!mounted) {
-    return <div className="w-9 h-9" />;
+    return <div className="ml-1 h-9 w-9" />;
   }
 
   const cycle = () => {
@@ -24,16 +24,16 @@ export function ThemeToggle() {
   return (
     <button
       onClick={cycle}
-      className="p-2 rounded-full bg-stone-100 dark:bg-stone-800 text-stone-800 dark:text-stone-100 hover:bg-stone-200 dark:hover:bg-stone-700 border border-stone-200 dark:border-stone-700 shadow-sm active:scale-[0.97] transition-[background-color,transform] duration-150 ease-out"
+      className="ml-1 rounded-full border-[1.5px] border-ink p-2 text-ink transition-[background-color,color,transform] duration-150 ease-out hover:bg-ink hover:text-paper active:scale-[0.97]"
       aria-label={`Current theme: ${theme}. Click to switch.`}
       title={theme === "system" ? "System" : theme === "dark" ? "Dark" : "Light"}
     >
       {theme === "system" ? (
-        <Monitor size={18} className="text-stone-500 dark:text-stone-300" />
+        <Monitor size={16} />
       ) : theme === "dark" ? (
-        <Sun size={18} className="text-amber-400" />
+        <Sun size={16} />
       ) : (
-        <Moon size={18} className="text-stone-600" />
+        <Moon size={16} />
       )}
     </button>
   );