dock: Fix dock launcher button persistence

quickshell/Common/SessionData.qml

@@ -758,6 +758,11 @@ Singleton {
         saveSettings();
     }
 
+    function setDockLauncherPosition(position) {
+        dockLauncherPosition = position;
+        saveSettings();
+    }
+
     function addPinnedApp(appId) {
         if (!appId)
             return;

quickshell/Common/settings/SessionSpec.js

@@ -39,6 +39,7 @@ var SPEC = {
     weatherCoordinates: { def: "40.7128,-74.0060" },
 
     pinnedApps: { def: [] },
+    dockLauncherPosition: { def: 0 },
     hiddenTrayIds: { def: [] },
     recentColors: { def: [] },
     showThirdPartyPlugins: { def: false },