feat: show last-run duration on the groups list

groups_index attaches last_duration_s from the latest group run; groups.html
renders it as a new right-aligned duration column (— when never run).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pipekit/web/app.py

@@ -1333,9 +1333,11 @@ def groups_index(request: Request):
         if recent:
             g["last_run_at"] = recent[0]["started_at"]
             g["last_status"] = recent[0]["status"]
+            g["last_duration_s"] = recent[0]["duration_s"]
         else:
             g["last_run_at"] = None
             g["last_status"] = None
+            g["last_duration_s"] = None
     return _templates.TemplateResponse(
         request, "groups.html",
         _ctx(groups=groups),

pipekit/web/templates/groups.html

@@ -19,6 +19,7 @@
                     <th>name</th>
                     <th>members</th>
                     <th>last run</th>
+                    <th style="width:7em;text-align:right">duration</th>
                     <th style="width:9em">status</th>
                     <th></th>
                 </tr>
@@ -29,6 +30,7 @@
                     <td><a href="/groups/{{ g.id }}"><strong>{{ g.name }}</strong></a></td>
                     <td class="mono">{{ g.member_count }}</td>
                     <td class="mono">{{ g.last_run_at | localtime }}</td>
+                    <td class="mono" style="text-align:right">{{ g.last_duration_s | duration }}</td>
                     <td>
                         {% if g.last_status %}
                         <span class="pill {{ g.last_status }}">{{ g.last_status }}</span>