Nav, safety, pillars updates

- Nav: all section links are absolute (/#section) - fixes about page back-nav
- Nav: add Environment link
- Safety: "I built" not "we built"; crisis hotline announcement; crisis line coming
- Pillars: rename Learns -> Sharpens with opaque copy that doesn't reveal mechanism

src/nav.el

@@ -11,11 +11,12 @@ fn nav() -> String {
   <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=\"#safety\"        class=\"nav-link\">Safety</a>
-      <a href=\"#pricing\"       class=\"nav-link\">Pricing</a>
-      <a href=\"#enterprise\"    class=\"nav-link\">Enterprise</a>
+      <a href=\"/#how-it-works\" class=\"nav-link\">How it works</a>
+      <a href=\"/#mission\"       class=\"nav-link\">Mission</a>
+      <a href=\"/#safety\"        class=\"nav-link\">Safety</a>
+      <a href=\"/#environmental\" class=\"nav-link\">Environment</a>
+      <a href=\"/#pricing\"       class=\"nav-link\">Pricing</a>
+      <a href=\"/#enterprise\"    class=\"nav-link\">Enterprise</a>
       <a href=\"/about\"         class=\"nav-link\">About</a>
       <a href=\"#share\"         class=\"nav-link cta\">Share Neuron →</a>
       <a href=\"#pricing\"       class=\"nav-cta\">Get Access</a>