Unify nav across all pages; broaden safety section

- about, terms, enterprise_terms now all import and use shared nav()
- Any future nav change propagates everywhere automatically
- Remove Docs from nav (no docs yet)
- Safety: Hard Bell is for everyone, not just children - reframe copy,
  update cards and bottom callout to reflect universal applicability

src/about.el

@@ -5,22 +5,10 @@
 // hard things stated in a single clause and moved past. Short sentences
 // are structural punctuation - used sparingly, at genuine rupture only.
 
+from nav import { nav }
+
 fn about_page() -> String {
-    return "
-<nav id=\"nav\">
-  <div class=\"nav-inner\">
-    <a href=\"/\" class=\"nav-logo\" aria-label=\"Neuron home\"><img src=\"/assets/brand/neuron-wordmark-on-light.png\" srcset=\"/assets/brand/neuron-wordmark-on-light@2x.png 2x\" alt=\"Neuron\" height=\"28\"></a>
-    <div class=\"nav-links\">
-      <a href=\"/#how-it-works\" class=\"nav-link\">How it works</a>
-      <a href=\"/#mission\"       class=\"nav-link\">Mission</a>
-      <a href=\"/#pricing\"       class=\"nav-link\">Pricing</a>
-      <a href=\"/#enterprise\"    class=\"nav-link\">Enterprise</a>
-      <a href=\"/docs\"           class=\"nav-link\">Docs</a>
-      <a href=\"/about\"          class=\"nav-link cta\" aria-current=\"page\">About</a>
-      <a href=\"/#pricing\"       class=\"nav-cta\">Get Access</a>
-    </div>
-  </div>
-</nav>
+    return nav() + "
 
 <main id=\"about\" style=\"padding: clamp(7rem, 18vh, 11rem) 2.5rem clamp(5rem, 12vh, 8rem);\">
   <div style=\"max-width: 700px; margin: 0 auto;\">