Dropped the custom HTML navbar in favor of mdbook's built-in navigation.
This also resolved an issue where relative anchor links were incorrectly
appearing as entries in the mdbook sidebar.
Replaced the custom HTML/CSS blog with mdbook. Gained a sidebar for
navigating sections, subsections, and pages. Applied a sepia-tone,
monospace theme. Blog sections now populate from SUMMARY.md rather than
manually maintained HTML includes.
