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/styles.el

@@ -1401,32 +1401,12 @@ fn page_close() -> String {
   pollFoundingCount();
   setInterval(pollFoundingCount, 90000);
 
-  // Stripe checkout
+  // Checkout buttons — navigate to integrated payment page
   var checkoutBtns = document.querySelectorAll('[data-checkout]');
   checkoutBtns.forEach(function(btn) {
     btn.addEventListener('click', function() {
       var plan = btn.getAttribute('data-checkout');
-      var origText = btn.textContent;
-      btn.textContent = 'Loading...';
-      btn.disabled = true;
-      fetch('/api/checkout', {
-        method: 'POST',
-        headers: { 'Content-Type': 'application/json' },
-        body: JSON.stringify({ plan: plan })
-      })
-      .then(function(r) { return r.json(); })
-      .then(function(data) {
-        if (data.url) {
-          window.location.href = data.url;
-        } else {
-          btn.textContent = 'Error — try again';
-          btn.disabled = false;
-        }
-      })
-      .catch(function() {
-        btn.textContent = 'Error — try again';
-        btn.disabled = false;
-      });
+      window.location.href = '/checkout?plan=' + plan;
     });
   });