Improve action menu escape handling

Make the F11 action menu close through a shared close action so Escape and the explicit Close actions menu item follow the same path. Treat Escape-prefixed Up and Down events as close inputs while the action menu is active, which handles termbox InputAlt behavior after pressing Escape. Preserve and restore the user/channel tree selection across action menu open and close, and preserve selection across live tree rebuilds.

Tested with: GOCACHE=/tmp/barnard-go-cache go test ./...

ui.go

@@ -66,7 +66,7 @@ func (b *Barnard) UpdateInputStatus(status string) {
 		status = status[:17] + "..." + "]"
 	}
 	b.UiInputStatus.Text = status
-	b.UiTree.Rebuild()
+	b.RebuildUserChannelTreePreservingSelection()
 	b.Ui.Refresh()
 }