feat: Add book viewer at /book with shared design system

- Add html/index.html: book viewer with auto-discovering sidebar,
  prev/next navigation, keyboard shortcuts, and URL hash persistence
- Add html/book-page.css: shared stylesheet for all book pages derived
  from fabula-ultima-sheet.css (dark theme, CSS variables, Cinzel/
  Crimson Text fonts, common class styles)
- Add book.js entry point so webpack injects the shared CSS into the
  book viewer; update webpack.config.js for two entry points, split
  CSS chunk, CopyWebpackPlugin for book pages, and /book dev server
  rewrite rule
- Add scripts/strip_watermark.py: removes "Guest Customer (Order
  #52072168)" watermark artifacts from all 210 book pages
- Add scripts/restyle_book.py: strips per-page <style> blocks and
  injects <link rel="stylesheet" href="book-page.css"> into all pages
- Update Justfile deploy to scp -r dist/* for the new /book subtree

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

package-lock.json

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@@ -2599,6 +2637,24 @@
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@@ -5648,6 +5704,23 @@
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+      "license": "MIT",
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