73 short titles

[sirkitree]

Resolves #73

Add short titles for mobile/narrow viewports

• Added shortTitle field to book metadata in index.html files
• Updated .eleventy.js to include shortTitle in book collection data
• Modified sidebar.liquid to display shortTitle with fallback to full title
• Updated styles.scss to show shortTitle on narrow viewports (height <= 800px) and mobile (width <= 1440px)

This change improves readability of book titles in the sidebar when space is constrained, either due to narrow viewport height in desktop view or when the site switches to mobile layout. The shortTitle provides a more concise version while maintaining context.

[huntermacd]

Lookin' good, just need to make sure the short title visibility kicks in earlier.

[sirkitree]

Ok try that - increased from 800px to 920px