feat(docs): create sukr documentation site with fixes

Self-documenting docs site built with sukr itself (dogfooding):

Core changes:
- Rename package from nrd-sh to sukr
- Move personal site to sites/nrd.sh/
- Update AGENTS.md and README.md

Documentation site (docs/):
- Add site.toml with sukr.io base URL
- Create docs-specific templates with sidebar navigation
- Add dark theme CSS with syntax highlighting colors
- Document all features: templates, sections, syntax highlighting,
  mermaid diagrams, and LaTeX math rendering

Bug fixes:
- Render individual pages for all sections (not just blog type)
- Add #[source] error chaining for Tera template errors
- Print full error chain in main() for better debugging

docs/content/features/templates.md

@@ -10,7 +10,7 @@ sukr uses [Tera](https://tera.netlify.app/), a Jinja2-like templating engine. Te
 
 ## Template Directory Structure
 
-```
+```text
 templates/
 ├── base.html               # Shared layout (required)
 ├── page.html               # Standalone pages