feat: narrative streaming via SSE with assistant_turn event

chat/templates/chat.html

@@ -1,14 +1,18 @@
 {% extends "layout.html" %}
 {% block title %}{{ host_bot.name }} - chat{% endblock %}
 {% block content %}
-<div class="chat-shell" data-chat-id="{{ chat.id }}">
+<div class="chat-shell" data-chat-id="{{ chat.id }}"
+     hx-ext="sse"
+     sse-connect="/chats/{{ chat.id }}/events">
   <header class="chat-header">
     <h1>{{ host_bot.name }}</h1>
     <div class="chat-meta muted">{{ chat.time }}</div>
     <button class="drawer-toggle" type="button" aria-controls="drawer" aria-expanded="false">Drawer</button>
   </header>
 
-  <section class="timeline" id="timeline">
+  <section class="timeline" id="timeline"
+           sse-swap="turn_html"
+           hx-swap="beforeend">
     {% if not turns %}
     <p class="muted">No turns yet. Start typing below.</p>
     {% else %}