Center the usage pill like every other tenant of the bar

Claude-Session: https://claude.ai/code/session_01Ms2FbjQy31TVf3CEvQhGM8

config/dot/quickshell/modules/bar/Bar.qml

@@ -112,7 +112,9 @@ PanelWindow {
                 screen: root.screen
             }
 
-            AgentUsageWidget {}
+            AgentUsageWidget {
+                anchors.verticalCenter: parent.verticalCenter
+            }
 
             VitalsWidget {
                 anchors.verticalCenter: parent.verticalCenter