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/main.el

@@ -40,6 +40,8 @@ from about            import { about_page }
 from founding_badge   import { founding_badge, founding_badge_css }
 from terms            import { terms_page }
 from enterprise_terms import { enterprise_terms_page }
+from checkout        import { checkout_page }
+from safety          import { safety }
 
 // ── Founding counter ──────────────────────────────────────────────────────────
 
@@ -78,6 +80,7 @@ fn page(sold: Int, total: Int) -> String {
         + enterprise()
         + mission()
         + local_first()
+        + safety()
         + environmental()
         + pricing(sold, total)
         + viral()
@@ -131,6 +134,42 @@ fn handle_request(method: String, path: String, body: String) -> String {
         return "{\"__status__\":404,\"error\":\"not found\"}"
     }
 
+    // ── Checkout page ─────────────────────────────────────────────────────────
+    if str_starts_with(path, "/checkout") {
+        let plan: String = "founding"
+        if str_contains(path, "plan=professional") {
+            plan = "professional"
+        }
+        let pub_key: String = state_get("__stripe_publishable_key__")
+        return page_open() + checkout_page(plan, pub_key) + page_close()
+    }
+
+    // ── Stripe payment intent ─────────────────────────────────────────────────
+    if str_eq(path, "/api/payment-intent") {
+        let stripe_key: String = state_get("__stripe_secret_key__")
+        if str_eq(stripe_key, "") {
+            return "{\"__status__\":503,\"error\":\"Stripe not configured\"}"
+        }
+        let plan: String = "founding"
+        if str_contains(body, "\"professional\"") {
+            plan = "professional"
+        }
+        let amount: String = "19900"
+        if str_eq(plan, "professional") {
+            amount = "1900"
+        }
+        let pi_body: String = "amount=" + amount
+            + "&currency=usd"
+            + "&payment_method_types[]=card"
+            + "&metadata[plan]=" + plan
+        let response: String = http_post_form_auth(
+            "https://api.stripe.com/v1/payment_intents",
+            stripe_key,
+            pi_body
+        )
+        return response
+    }
+
     // ── Health check ──────────────────────────────────────────────────────────
     if str_eq(path, "/api/health") {
         return "{\"status\":\"ok\",\"service\":\"neuron-landing\"}"
@@ -279,10 +318,12 @@ state_set("__founding_total__",              int_to_str(FOUNDING_TOTAL))
 
 // Stripe config from environment.
 let stripe_key: String = env("STRIPE_SECRET_KEY")
+let stripe_pub_key: String = env("STRIPE_PUBLISHABLE_KEY")
 let stripe_price_founding: String = env("STRIPE_PRICE_FOUNDING")
 let stripe_price_professional: String = env("STRIPE_PRICE_PROFESSIONAL")
 let license_api_url: String = env("NEURON_LICENSE_API_URL")
 state_set("__stripe_secret_key__",        stripe_key)
+state_set("__stripe_publishable_key__",   stripe_pub_key)
 state_set("__stripe_price_founding__",    stripe_price_founding)
 state_set("__stripe_price_professional__", stripe_price_professional)
 state_set("__license_api_url__",          license_api_url)