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.

docs/content/features/mermaid.md

@@ -0,0 +1,70 @@
+---
+title: Mermaid Diagrams
+description: Build-time diagram rendering with Mermaid
+weight: 4
+---
+
+# Mermaid Diagrams
+
+sukr renders Mermaid diagrams at build time, producing inline SVG. No client-side JavaScript required.
+
+## Usage
+
+Use fenced code blocks with `mermaid` language:
+
+````markdown
+```mermaid
+graph LR
+    A[Input] --> B[Process]
+    B --> C[Output]
+```
+````
+
+## Supported Diagram Types
+
+| Type      | Status          | Description                               |
+| --------- | --------------- | ----------------------------------------- |
+| Flowchart | ✅ Full support | Flow diagrams with nodes and edges        |
+| Graph     | ✅ Full support | Directed/undirected graphs                |
+| Sequence  | ⚠️ Partial      | Sequence diagrams (some layouts may vary) |
+| State     | ⚠️ Partial      | State machine diagrams                    |
+| Class     | ⚠️ Partial      | UML class diagrams                        |
+
+> **Note:** Some complex diagram types may have layout differences compared to the JavaScript renderer. Flowcharts and basic graphs work reliably.
+
+## How It Works
+
+1. During Markdown parsing, `mermaid` code blocks are intercepted
+2. The Mermaid definition is parsed and rendered to SVG
+3. The SVG is inlined directly in the HTML output
+4. No JavaScript or external resources needed
+
+## Example
+
+```mermaid
+graph TD
+    A[Markdown] --> B{sukr}
+    B --> C[HTML]
+    B --> D[SVG Diagrams]
+    B --> E[Highlighted Code]
+```
+
+## Styling
+
+Mermaid SVGs inherit your CSS variables. Customize the look by targeting SVG elements:
+
+```css
+.mermaid svg {
+  max-width: 100%;
+  height: auto;
+}
+
+.mermaid .node rect {
+  fill: var(--bg-sidebar);
+  stroke: var(--accent);
+}
+```
+
+## Fallback
+
+If a diagram fails to render (complex diagrams, syntax errors), the original code block is preserved with an error comment.

docs/content/features/sections.md

@@ -12,7 +12,7 @@ sukr automatically discovers sections from your content directory structure.
 
 A section is any directory under `content/` that contains an `_index.md` file:
 
-```
+```text
 content/
 ├── _index.md           # Homepage (not a section)
 ├── about.md            # Standalone page

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