test(web): run the subagent-conversation e2e against the locale-aware copy

The ui-subagent catalog and read-only composer copy moved from hardcoded
Chinese to the locale-aware `subagent` namespace, so an en-US headless
browser now renders English. The e2e's selectors and goldens still
asserted the old hardcoded Chinese strings, leaving the scenario unable
to find the catalog trigger.

Convert the selectors to the default (en-US) render and re-record the
catalog goldens (ui, tree, nested) in English. The locale-aware parts of
the remaining goldens were already English (recorded under the en-US
default), so sidebar and fork are untouched.

apps/web/tests/snapshots/subagent-conversation/ui.expected.md

@@ -3,8 +3,8 @@
     - button "Ask a research subagent to"
     - text: /
     - button "event-sourcing researcher" [disabled]
-  - button "1 个子代理":
-    - text: 1 个子代理
+  - button "1 subagents":
+    - text: 1 subagents
     - img
   - tablist:
     - tab "Chat" [selected]