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

manifest.el

@@ -0,0 +1,12 @@
+package "neuron-landing" {
+    version "1.0.0"
+    description "Neuron marketing landing page server"
+    authors ["Will Anderson <will@neurontechnologies.ai>"]
+    edition "2026"
+}
+
+build {
+    target "release"
+    entry "src/main.el"
+    output "dist/"
+}