Fix initStripe load order, subscription webhook email extraction, chat textarea UX

- checkout.el: swap stripe_el_script before auth_script so initStripe is
  defined when Supabase auth fires onAuthStateChange on page load
- main.el: fix Stripe webhook email extraction for checkout.session.completed
  (subscription) events — customer_details is nested at data.object level,
  not at root; previous code only worked for payment_intent.succeeded
- page_close.c: replace <input type="text"> with <textarea rows="1"> in
  the chat widget input row so long questions are visible as you type
- page_css.c: update #neuron-demo-text CSS for textarea (resize:none,
  overflow:hidden, min/max-height, align-items:flex-end on row)
- chat-widget.el: add auto-resize event listener (grows up to ~4 lines),
  reset height to auto on send

src/checkout.el

@@ -341,7 +341,7 @@ fn checkout_page(plan: String, pub_key: String) -> String {
     let stripe_el_script: String = el_script_src("/js/checkout-stripe.js", true)
     let free_init_script: String = ""
 
-    return nav_html + main_html + supabase_script + stripe_script + style_html + auth_script + cfg_script + stripe_el_script + free_init_script
+    return nav_html + main_html + supabase_script + stripe_script + style_html + stripe_el_script + cfg_script + auth_script + free_init_script
 }
 
 fn checkout_style_html() -> String {