Manuscript theme overhaul: Newsreader headings, scholarly palette, hairline dividers

- Add Newsreader variable font (regular + italic) for headings, card titles, admonitions
- New palette: Midnight #2A3848, Crimson #750003, Paper White #FAF9F5, Ghost Grey #C3C6D5
- Hero title: 2.8rem Newsreader weight-300 with blue text-shadow glow
- Gradient hairline dividers on h1 and hr elements (ghost grey fading to transparent)
- Crimson accent for card hover links, active sidebar items, link hover states
- Muted scholarly icon tones on feature cards
- Paper-white page background with ghost-grey card borders
- Dark mode updated to match new palette

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

Author: hk-2029