feat: smart scroll — keep position when reading, badge for new messages

- Add pollMensajes() so wire:poll no longer force-scrolls to bottom
- MutationObserver detects new DOM nodes: auto-scrolls only if user
  is already at the bottom (within 80px threshold)
- Floating '↓ N mensaje nuevo' badge appears when new bot messages
  arrive while user is scrolled up; tap badge to jump to bottom
- scroll-chat event (emitted on button clicks/sends) still forces
  scroll since the user just took an action

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Http/Livewire/Chat/PublicChat.php

@@ -1225,7 +1225,7 @@ class PublicChat extends Component
         $this->mensajes = ChatMessage::where('conversation_id', $this->convId)
             ->orderBy('id')
             ->get()
-            ->map(fn($m) => [
+            ->map(fn ($m) => [
                 'tipo'       => $m->tipo,
                 'tipo_ui'    => $m->tipo_ui ?? 'text',
                 'contenido'  => $m->contenido,
@@ -1237,6 +1237,27 @@ class PublicChat extends Component
         $this->dispatchBrowserEvent('scroll-chat');
     }
 
+    // Llamado por wire:poll — igual que cargarMensajes pero sin forzar scroll
+    public function pollMensajes(): void
+    {
+        if (! $this->convId) {
+            return;
+        }
+
+        $this->mensajes = ChatMessage::where('conversation_id', $this->convId)
+            ->orderBy('id')
+            ->get()
+            ->map(fn ($m) => [
+                'tipo'       => $m->tipo,
+                'tipo_ui'    => $m->tipo_ui ?? 'text',
+                'contenido'  => $m->contenido,
+                'payload'    => $m->payload ?? [],
+                'created_at' => $m->created_at->format('H:i'),
+            ])
+            ->toArray();
+        // No dispatches scroll-chat — el MutationObserver del JS maneja el badge
+    }
+
     // ─────────────────────────────────────────────────────────
     // Helpers
     // ─────────────────────────────────────────────────────────