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>

scripts/pdf.js

@@ -0,0 +1,51 @@
+import puppeteer from 'puppeteer';
+import { resolve, dirname } from 'path';
+import { fileURLToPath } from 'url';
+import { access } from 'fs/promises';
+
+const __dir = dirname(fileURLToPath(import.meta.url));
+
+async function fileExists(path) {
+  try { await access(path); return true; } catch { return false; }
+}
+const root = resolve(__dir, '..');
+const inputPath = resolve(root, 'output', 'book.html');
+const outputPath = resolve(root, 'output', 'kaleidoskop.pdf');
+
+async function generate() {
+  try {
+    await access(inputPath);
+  } catch {
+    console.error('output/book.html not found — run `pnpm build` first');
+    process.exit(1);
+  }
+
+  // On ARM64 (e.g. WSL2 on Apple Silicon / Raspberry Pi), Puppeteer's bundled
+  // Chrome is x86-64 and won't run. Use the system Chromium instead:
+  //   sudo apt-get install -y chromium
+  const systemChromium = '/usr/bin/chromium';
+  const useSystem = await fileExists(systemChromium);
+
+  console.log(`Launching Puppeteer (${useSystem ? 'system Chromium' : 'bundled Chrome'})…`);
+  const browser = await puppeteer.launch({
+    headless: true,
+    ...(useSystem ? { executablePath: systemChromium } : {}),
+  });
+  const page = await browser.newPage();
+
+  await page.goto(`file://${inputPath}`, { waitUntil: 'networkidle0' });
+
+  // 8.75 × 8.75 inches = trim (8.5×8.5) + 0.125in bleed on each side
+  await page.pdf({
+    path: outputPath,
+    width: '8.75in',
+    height: '8.75in',
+    printBackground: true,
+    margin: { top: 0, bottom: 0, left: 0, right: 0 },
+  });
+
+  await browser.close();
+  console.log(`PDF written to output/kaleidoskop.pdf`);
+}
+
+generate().catch(err => { console.error(err); process.exit(1); });