Set up book project: Markdown→CSS→PDF pipeline for KDP

Adds the full authoring and build toolchain for "Das Kaleidoskop der
Schlummerwelten" — all 12 story content files in Markdown, Nunjucks
HTML templates, CSS print layout, and Puppeteer-based PDF generation
targeting Amazon KDP (8.5×8.5 in, 0.125in bleed).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/story-spread.html

@@ -0,0 +1,40 @@
+{% for scene in story.scenes %}
+{# ── Left page: full-bleed illustration ── #}
+<div class="page page--image" data-story="{{ story.number }}" style="
+  --color-primary: {{ story.palette.primary }};
+  --color-secondary: {{ story.palette.secondary }};
+  --color-text: {{ story.palette.text }};
+  --color-bg: {{ story.palette.background }};
+">
+  {% if scene.imageExists %}
+    <img
+      class="scene-image"
+      src="{{ scene.image }}"
+      alt="{{ scene.alt }}"
+    >
+  {% else %}
+    <div class="placeholder-image" style="background: {{ story.palette.primary }};">
+      <div class="placeholder-label">
+        <span class="placeholder-story">Geschichte {{ story.number }}</span>
+        <span class="placeholder-scene">{{ scene.alt }}</span>
+      </div>
+    </div>
+  {% endif %}
+</div>
+
+{# ── Right page: story text ── #}
+<div class="page page--text" data-story="{{ story.number }}" style="
+  --color-primary: {{ story.palette.primary }};
+  --color-secondary: {{ story.palette.secondary }};
+  --color-text: {{ story.palette.text }};
+  --color-bg: {{ story.palette.background }};
+">
+  <div class="text-page-inner">
+    {% if loop.first %}
+      <h2 class="story-title">{{ story.title }}</h2>
+    {% endif %}
+    <div class="scene-text">{{ scene.html | safe }}</div>
+    <div class="scene-ornament">✦</div>
+  </div>
+</div>
+{% endfor %}