fix(frontend): align zod v4 typings and defaults

frontend/src/test-setup.ts

@@ -46,10 +46,7 @@ function enhancedParse<T>(this: z.ZodType<T>, data: unknown): T {
  * @param data - The data to validate against the schema
  * @returns Safe parse result with success flag and data or error
  */
-function enhancedSafeParse<T>(
-  this: z.ZodType<T>,
-  data: unknown
-): z.SafeParseReturnType<unknown, T> {
+function enhancedSafeParse<T>(this: z.ZodType<T>, data: unknown) {
   const result = originalSafeParse.call(this, data);
   validationCount++;
 

frontend/src/validation.ts

@@ -22,7 +22,7 @@ export const UserSchema = z.object({
       theme: z.enum(['light', 'dark']).default('light'),
       notifications: z.boolean().default(true),
     })
-    .default({}),
+    .default({ theme: 'light', notifications: true }),
 });
 
 // Inferred types (no manual type definitions needed)