feat(nav): complete Tier 1 hierarchical navigation

Add config option [nav] nested (defaults false), update base.html
template with nested nav rendering, and add .nav-children CSS styling
for indented section children.

- Add NavConfig struct with nested: bool
- Template renders item.children in .nav-children div
- CSS: left border + indent for nested items

docs/site.toml

@@ -7,3 +7,6 @@ content   = "content"
 output    = "public"
 static    = "static"
 templates = "templates"
+
+[nav]
+nested = true

docs/static/style.css

@@ -94,6 +94,19 @@ body {
   color: var(--bg);
 }
 
+.sidebar .nav-children {
+  margin-left: 1rem;
+  padding-left: 0.5rem;
+  border-left: 1px solid var(--border);
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+}
+
+.sidebar .nav-children a {
+  font-size: 0.9rem;
+}
+
 .sidebar-footer {
   margin-top: auto;
   padding-top: 1rem;

docs/templates/base.html

@@ -34,8 +34,17 @@
       </label>
     </header>
     <nav>
-      {% for item in nav %}<a href="{{ prefix }}{{ item.path }}" {% if page_path==item.path %} class="active" {% endif
-        %}>{{ item.label }}</a>{% endfor %}
+      {% for item in nav %}
+      <a href="{{ prefix }}{{ item.path }}" {% if page_path==item.path %}class="active" {% endif %}>{{ item.label }}</a>
+      {% if config.nested_nav and item.children %}
+      <div class="nav-children">
+        {% for child in item.children %}
+        <a href="{{ prefix }}{{ child.path }}" {% if page_path==child.path %}class="active" {% endif %}>{{ child.label
+          }}</a>
+        {% endfor %}
+      </div>
+      {% endif %}
+      {% endfor %}
     </nav>
     <footer class="sidebar-footer">
       <a href="https://github.com/nrdxp/sukr">GitHub</a>

src/config.rs

@@ -17,6 +17,17 @@ pub struct SiteConfig {
     /// Path configuration (all optional with defaults).
     #[serde(default)]
     pub paths: PathsConfig,
+    /// Navigation configuration.
+    #[serde(default)]
+    pub nav: NavConfig,
+}
+
+/// Navigation configuration.
+#[derive(Debug, Deserialize, Default)]
+#[serde(default)]
+pub struct NavConfig {
+    /// Whether to display nested navigation (default: false).
+    pub nested: bool,
 }
 
 /// Path configuration with sensible defaults.

src/template_engine.rs

@@ -121,6 +121,8 @@ pub struct ConfigContext {
     pub title: String,
     pub author: String,
     pub base_url: String,
+    /// Whether to display nested navigation
+    pub nested_nav: bool,
 }
 
 impl From<&SiteConfig> for ConfigContext {
@@ -129,6 +131,7 @@ impl From<&SiteConfig> for ConfigContext {
             title: config.title.clone(),
             author: config.author.clone(),
             base_url: config.base_url.clone(),
+            nested_nav: config.nav.nested,
         }
     }
 }