feat(training): delete group button (admin only) on Training page

- Backend DELETE /api/groups/<gid> (admin, own-org enforced via _get_owned_group);
  cascades removal of the group's sessions. GroupStore.delete added.
- Training.vue: each group card gets a trash (Trash2 line icon) delete button shown only
  to admins (auth.isAdmin); confirm dialog; @click.stop so it doesn't navigate. Card
  restructured so the delete button is not inside the clickable router-link.
- test_user_journey: trainee cannot delete (403), admin deletes, group gone (404).
All suites pass. Rebuilt dist.

backend/app/api/group_routes.py

@@ -324,6 +324,28 @@ def update_persona(gid: str, pid: str):
     return jsonify({"persona": strip_secret_fields(full)})
 
 
+@groups_bp.delete("/<gid>")
+@require_auth
+@require_roles("admin")
+def delete_group(gid: str):
+    """Delete a persona group (admin only, own org)."""
+    s = _stores()
+    group = _get_owned_group(s, gid)  # also enforces tenant org (super_admin global)
+    s["groups"].delete(gid)
+    # cascade: also remove finished/active sessions for this group's personas
+    try:
+        sess = s.get("session_store")
+        if sess and hasattr(sess, "sessions"):
+            for r in sess.sessions.all():
+                if r.get("group_id") == gid:
+                    key = r.get("id") or r.get("sid")
+                    if key:
+                        sess.sessions.delete(key)
+    except Exception:
+        pass
+    return jsonify({"ok": True, "deleted": gid})
+
+
 @groups_bp.post("/<gid>/reanalyze")
 @require_auth
 @require_roles("admin")