fix: resize images to 2550 px (300 DPI) at build time to prevent WSL2 OOM crash

4096×4096 source images decoded simultaneously by Chromium consumed ~3.2 GB,
exhausting WSL2 RAM. Build now uses sharp to downsize to 2550×2550 (8.5 in ×
300 DPI) into output/resized/ before Puppeteer loads them, cutting in-memory
footprint to ~1.25 GB. Also adds all story images (01–12) to the repository.

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

.gitignore

@@ -1,6 +1,7 @@
 .claude/
 node_modules/
 output/book.html
+output/resized/
 output/cover.html
 output/book-meta.json
 # Interior PDF is large (~100 MB with placeholder pages) — excluded from git.