* render alt text as image captions

* fix: nested list rendering

* implemented and documented logging

* remove jump to slide

fix: help line toggle

* added theme registry with 7 built-in themes (default, dark, light, monokai, dracula, solarized_dark, nord)
* automatic column width calculation for tables with proper Unicode borders
* Update CLI to load themes from registry based on frontmatter, CLI flags, or environment variables
* drafted theme documentation with examples and descriptions