feat(demo): cap chat input at 8000 chars (~2000 tokens)

src/js/chat-widget.el

@@ -236,6 +236,14 @@ fn main() -> Void {
     if (!input || btn.disabled) return;
     var msg = input.value.trim();
     if (!msg) return;
+    var MAX_CHARS = 8000;
+    if (msg.length > MAX_CHARS) {
+      if (input) {
+        input.style.outline = '2px solid #e53e3e';
+        setTimeout(function() { input.style.outline = ''; }, 2000);
+      }
+      return;
+    }
     input.value = '';
     btn.disabled = true;
     addMsg('user', msg);

src/styles.el

@@ -1997,7 +1997,7 @@ fn page_close() -> String {
   <div id="neuron-demo-messages"></div>
   <div id="neuron-demo-turnstile" style="padding:0.75rem 1rem 0;transition:opacity 0.6s,max-height 0.6s;overflow:hidden;max-height:80px"></div>
   <div id="neuron-demo-input-row" style="display:none">
-    <input type="text" id="neuron-demo-text" placeholder="Ask me anything..." autocomplete="off">
+    <input type="text" id="neuron-demo-text" placeholder="Ask me anything..." autocomplete="off" maxlength="8000">
     <button id="neuron-demo-send" onclick="neuronDemoSend()">Send</button>
   </div>
 </div>