Rewrite landing to El component architecture

Full El component split: nav, hero, pillars, inference, pricing, footer, about,
enterprise, mission, viral, local_first, comparison, efficiency, environmental.

- About page rewritten first-person (Will's voice), photo included, no product spoilers
- Stripe checkout wired: env() reads STRIPE_SECRET_KEY/PRICE_* at startup
- Minor parent-onboarding callout added to pricing section
- Inference pricing: "at cost" removed, now "priced below competitors"
- Nav: wordmark image, About link active on /about
- .gitignore: excludes .env, dist/, generated HTML

src/nav.el

@@ -0,0 +1,26 @@
+// components/nav.el — Top navigation bar.
+//
+// Returns an HTML string. Server-rendered, no JavaScript required for
+// the nav structure itself. Scroll-based opacity is CSS-only via
+// :has() and scroll-driven animations where supported; we default to
+// a clean transparent state that looks great on first load.
+
+fn nav() -> 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=\"/about\"         class=\"nav-link\">About</a>
+      <a href=\"/docs\"          class=\"nav-link\">Docs</a>
+      <a href=\"#share\"         class=\"nav-link cta\">Share Neuron →</a>
+      <a href=\"#pricing\"       class=\"nav-cta\">Get Access</a>
+    </div>
+  </div>
+</nav>
+"
+}