fix(webapp): fallback dashboard preferences get a fresh object per caller

A shallow copy shared the inner projects container between every user
without saved preferences on the process.

Author: kathiekiwi

apps/webapp/app/utils/dashboardPreferences.ts

@@ -64,24 +64,28 @@ const DashboardPreferences = z.object({
 
 export type DashboardPreferences = z.infer<typeof DashboardPreferences>;
 
-const DEFAULT_PREFERENCES: DashboardPreferences = {
-  version: "1",
-  projects: {},
-};
+/* A function, not a shared constant: the writers mutate through these objects,
+   so each caller needs its own container */
+function defaultPreferences(): DashboardPreferences {
+  return {
+    version: "1",
+    projects: {},
+  };
+}
 
 /** Parses the stored JSON, falling back to defaults on missing or invalid data. */
 export function parseDashboardPreferences(
   data?: any | null,
   onError?: (error: z.ZodError) => void
 ): DashboardPreferences {
   if (!data) {
-    return { ...DEFAULT_PREFERENCES };
+    return defaultPreferences();
   }
 
   const result = DashboardPreferences.safeParse(data);
   if (!result.success) {
     onError?.(result.error);
-    return { ...DEFAULT_PREFERENCES };
+    return defaultPreferences();
   }
 
   return result.data;