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/math.md

@@ -0,0 +1,81 @@
+---
+title: Math Rendering
+description: Build-time LaTeX math with KaTeX
+weight: 5
+---
+
+# Math Rendering
+
+sukr renders LaTeX math expressions at build time using KaTeX, producing static HTML and CSS. No client-side JavaScript required.
+
+## Inline Math
+
+Use single dollar signs for inline math:
+
+```markdown
+The quadratic formula is $x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$.
+```
+
+Renders as: The quadratic formula is $x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$.
+
+## Display Math
+
+Use double dollar signs for display (block) math:
+
+```markdown
+$$
+E = mc^2
+$$
+```
+
+Or fence with `math` language:
+
+````markdown
+```math
+\int_0^\infty e^{-x^2} dx = \frac{\sqrt{\pi}}{2}
+```
+````
+
+## Supported Features
+
+KaTeX supports a large subset of LaTeX math:
+
+- Greek letters: `$\alpha, \beta, \gamma$`
+- Fractions: `$\frac{a}{b}$`
+- Subscripts/superscripts: `$x_i^2$`
+- Summations: `$\sum_{i=1}^{n} i$`
+- Integrals: `$\int_a^b f(x)\,dx$`
+- Matrices: `$\begin{pmatrix} a & b \\ c & d \end{pmatrix}$`
+- And much more...
+
+## How It Works
+
+1. Math delimiters (`$...$`, `$$...$$`) are detected during parsing
+2. KaTeX renders the expression to HTML + CSS
+3. Required fonts are embedded inline
+4. Output is pure HTML—no JavaScript
+
+## Styling
+
+KaTeX output uses semantic classes. Customize appearance:
+
+```css
+.katex {
+  font-size: 1.1em;
+}
+
+.katex-display {
+  margin: 1.5em 0;
+  overflow-x: auto;
+}
+```
+
+## Error Handling
+
+Invalid LaTeX produces an error message inline rather than breaking the build:
+
+```markdown
+$\invalid{command}$
+```
+
+Renders with a red error indicator showing what went wrong.