test(chat): realign the stale subagent golden snapshot

27c20389a made a nested tool_use_complete keep the parent's chatState
rather than dropping the session back to `thinking`, so a subagent's
inner tool call no longer clears the parent Task's progress indicator.
That was the intended fix, but the golden fixture still pinned the old
`thinking` value and the two subagent scenarios have failed since —
masked until now because localStorage was taking the whole file down
first.

Regenerating touches exactly one line, and produces an identical file
from a clean HEAD, confirming this is fixture staleness rather than a
behaviour change of ours.

Local desktop suite is now fully green: 304 files, 4202 passed.

desktop/src/stores/__fixtures__/chat-store.golden.json

@@ -991,7 +991,7 @@
             "parentToolUseId": "toolu_parent_agent"
           }
         ],
-        "chatState": "thinking",
+        "chatState": "tool_executing",
         "streamingText": "",
         "streamingToolInput": "",
         "activeToolUseId": null,