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

dist/page_css.c

@@ -1764,6 +1764,7 @@ el_val_t page_css(void) {
         "\n"
         "    #neuron-demo-input-row {\n"
         "      display: flex;\n"
+        "      align-items: flex-end;\n"
         "      border-top: 1px solid var(--border);\n"
         "      flex-shrink: 0;\n"
         "    }\n"
@@ -1771,11 +1772,16 @@ el_val_t page_css(void) {
         "      flex: 1;\n"
         "      font-family: var(--body);\n"
         "      font-size: 0.875rem;\n"
+        "      line-height: 1.5;\n"
         "      color: var(--t1);\n"
         "      background: var(--bg);\n"
         "      border: none;\n"
         "      outline: none;\n"
         "      padding: 0.875rem 1rem;\n"
+        "      resize: none;\n"
+        "      overflow: hidden;\n"
+        "      min-height: 2.75rem;\n"
+        "      max-height: 7.5rem;\n"
         "    }\n"
         "    #neuron-demo-text::placeholder { color: var(--t3); }\n"
         "    #neuron-demo-send {\n"