Add layout_settled to screenshot_triggers enum in events plan

The screenshot_triggers enum included all computed events (network_idle,
scroll_settled, navigation_settled) except layout_settled. This was an
oversight since layout_settled is a distinct computed meta-event and should
be available as a screenshot trigger for capturing visual stability moments
independently of network activity.

Author: cursoragent

.cursor/plans/2026-02-05-events.md

@@ -201,7 +201,7 @@ EventCaptureConfig:
       type: array
       items:
         type: string
-        enum: [error, page_load, navigation_settled, scroll_settled, network_idle]
+        enum: [error, page_load, navigation_settled, scroll_settled, network_idle, layout_settled]
       description: Which events trigger a screenshot. Default [error, navigation_settled]
     targets:
       type: boolean