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/globals.css

@@ -30,6 +30,13 @@
     --ease-out: cubic-bezier(0.23, 1, 0.32, 1);
     --ease-in-out: cubic-bezier(0.77, 0, 0.175, 1);
     --ease-drawer: cubic-bezier(0.32, 0.72, 0, 1);
+
+    /* Plakat-Design (RGB-Kanäle, damit Tailwind-Deckkraft funktioniert) */
+    --plakat-red: 232 64 47;
+    --plakat-ink: 20 12 11;
+    --plakat-paper: 246 243 241;
+    --plakat-paper-2: 235 230 226;
+    --plakat-ok: 31 157 99;
 }
 
 .dark {
@@ -52,12 +59,18 @@
     --border: #44403c;
     --input: #292524;
     --ring: #d6d3d1;
+
+    /* Tinte und Papier tauschen die Rollen, das Rot bleibt */
+    --plakat-ink: 243 238 233;
+    --plakat-paper: 21 16 15;
+    --plakat-paper-2: 36 30 28;
+    --plakat-ok: 60 199 138;
 }
 
 body {
-    background: var(--background);
-    color: var(--foreground);
-    font-family: "Inter", sans-serif;
+    background: rgb(var(--plakat-paper));
+    color: rgb(var(--plakat-ink));
+    font-family: var(--font-geist), "Helvetica Neue", Arial, sans-serif;
     margin: 0;
     padding: 0;
     overflow-x: hidden;
@@ -70,8 +83,8 @@ body {
 
 /* Custom Selection */
 ::selection {
-    background: var(--primary); /* Rich brown for better contrast */
-    color: var(--primary-foreground); /* Off-white */
+    background: rgb(var(--plakat-ink));
+    color: rgb(var(--plakat-paper));
 }
 
 /* Smooth Scrolling */
@@ -135,18 +148,11 @@ h3,
 h4,
 h5,
 h6 {
-    font-family: var(--font-playfair), Georgia, serif;
+    font-family: var(--font-bricolage), "Avenir Next", "Segoe UI", sans-serif;
     letter-spacing: -0.02em;
     font-weight: 700;
-    color: var(--foreground);
 }
 
-/* Improve text contrast - using foreground variable for WCAG AA compliance */
-p,
-span,
-div {
-    color: var(--foreground); /* #3e2723 - meets WCAG AA standards */
-}
 
 /* Hide scrollbar but keep functionality */
 ::-webkit-scrollbar {