feat(docs): create sukr documentation site

Self-documenting docs site built with sukr itself (dogfooding):
- docs/site.toml with sukr.io base URL
- docs-specific templates with sidebar navigation
- Dark theme CSS, responsive layout
- Documentation: getting-started, configuration, features

Also: improved error chaining for better template debugging

docs/content/getting-started.md

@@ -0,0 +1,77 @@
+---
+title: Getting Started
+description: Install sukr and build your first site
+weight: 1
+---
+
+# Getting Started
+
+This guide walks you through installing sukr and creating your first static site.
+
+## Installation
+
+### From source (recommended)
+
+```bash
+git clone https://github.com/nrdxp/sukr
+cd sukr
+cargo install --path .
+```
+
+### With Nix
+
+```bash
+nix build github:nrdxp/sukr
+./result/bin/sukr --help
+```
+
+## Create Your First Site
+
+### 1. Create directory structure
+
+```bash
+mkdir my-site && cd my-site
+mkdir -p content templates static
+```
+
+### 2. Create configuration
+
+Create `site.toml`:
+
+```toml
+title    = "My Site"
+author   = "Your Name"
+base_url = "https://example.com"
+```
+
+### 3. Create homepage
+
+Create `content/_index.md`:
+
+```markdown
+---
+title: Welcome
+description: My awesome site
+---
+
+# Hello, World!
+
+This is my site built with sukr.
+```
+
+### 4. Create templates
+
+Copy the default templates from the sukr repository, or create your own Tera templates.
+
+### 5. Build
+
+```bash
+sukr
+```
+
+Your site is now in `public/`.
+
+## Next Steps
+
+- Learn about [Configuration](configuration.html)
+- Explore [Features](features/index.html)