Add integrated checkout, child safety section, and content polish

- checkout.el: Custom Stripe Payment Element page at /checkout?plan=...
- safety.el: Hard Bell and emergency routing architecture section
- main.el: Wire checkout + safety, /api/payment-intent, STRIPE_PUBLISHABLE_KEY
- enterprise_terms.el: Add nav bar (was missing, page had no navigation)
- styles.el: Checkout buttons now link to integrated page, not hosted Stripe
- El runtime: Auto-detect HTML responses, serve text/html vs application/json
- footer.el: Wordmark image centered above "Built Different." tagline
- environmental.el: Replace SQLite with custom on-device storage
- enterprise.el: Replace SQLite with custom on-device storage
- pricing.el: Local models degraded performance note near Ollama feature
- about.el: "left home at fifteen", remove programming language mention

src/about.el

@@ -36,7 +36,7 @@ fn about_page() -> String {
       <img src=\"/assets/will.png\" alt=\"Will Anderson\" style=\"width: 160px; height: 160px; border-radius: 50%; object-fit: cover; flex-shrink: 0;\">
       <div style=\"flex: 1; min-width: 260px;\">
         <p style=\"font-family: var(--body); font-weight: 300; font-size: clamp(0.9rem, 1.5vw, 1.0625rem); color: var(--t2); line-height: 1.9; margin-bottom: 1.5rem;\">
-          I grew up in Fort Smith, Arkansas, in the kind of instability where home is a moving target &#8212; roughly thirty addresses before I was fifteen, parents struggling with addiction, the material precarity that comes with all of that. I left when I was old enough to go, stayed with friends until I finished high school, found my way to college. At fourteen I&#39;d already found software, writing C++ at the public library because it was the first thing in my life that responded to precision with correctness, and that property turned out to matter more to me than almost anything else.
+          I grew up in Fort Smith, Arkansas, in the kind of instability where home is a moving target &#8212; roughly thirty addresses before I was fifteen, parents struggling with addiction, the material precarity that comes with all of that. I left home at fifteen, stayed with friends until I finished high school, found my way to college. At fourteen I&#39;d already found software, writing C++ at the public library because it was the first thing in my life that responded to precision with correctness, and that property turned out to matter more to me than almost anything else.
         </p>
       </div>
     </div>
@@ -84,7 +84,7 @@ fn about_page() -> String {
     <div class=\"reveal\" style=\"margin-bottom: 3rem;\">
       <p class=\"label\" style=\"margin-bottom: 1.25rem;\">What I built</p>
       <p style=\"font-family: var(--body); font-weight: 300; font-size: clamp(0.9rem, 1.5vw, 1.0625rem); color: var(--t2); line-height: 1.9; margin-bottom: 1.5rem;\">
-        Neuron is what I built in response to that. Not a startup in the traditional sense &#8212; no team, no funding, no press release &#8212; one person, nearly two years of work, and a conviction that this can be done differently. I wrote the programming language the core runs in, I wrote the memory architecture, I built the inference infrastructure, because the tools that existed weren&#39;t sufficient for what I was trying to build and so I built those too.
+        Neuron is what I built in response to that. Not a startup in the traditional sense &#8212; no team, no funding, no press release &#8212; one person, nearly two years of work, and a conviction that this can be done differently. I wrote the memory architecture, I built the inference infrastructure, because the tools that existed weren&#39;t sufficient for what I was trying to build and so I built those too.
       </p>
       <p style=\"font-family: var(--body); font-weight: 300; font-size: clamp(0.9rem, 1.5vw, 1.0625rem); color: var(--t2); line-height: 1.9;\">
         Use it long enough and you&#39;ll understand why I couldn&#39;t have gotten there on top of existing infrastructure. Some things have to be built from the ground up to be built right.