Merge branch 'stack/agent-profiles-5-web-ui' into stack/agent-profiles-8-authoring

Authoring meets standing mounts: write() and remove() drop the standing
pointer so the NEXT session composes the edited roster, while every session
already joined keeps the generation it runs on — a superseded generation is
never disposed while the process lives. The settings-dialog golden re-records
with this layer's Agent Preset nav entry, which the incoming layer-3 record
had overwritten.

apps/web/tests/snapshots/models-settings/declared.expected.md

@@ -7,6 +7,9 @@
     - button "模型":
       - img
       - text: 模型
+    - button "Agent 预设":
+      - img
+      - text: Agent 预设
   - button "打开配置文件"
   - button "关闭":
     - img