fix(useForm): update defaults and remember logic

Use deep set for updating multiple default fields to handle nested keys correctly. Also, update remember logic to use formData instead of getData() for consistency.

Author: brodienguyen

packages/svelte5/src/useForm.svelte.ts

@@ -143,7 +143,9 @@ export default function useForm<TForm extends FormDataType<TForm>>(
       } else {
         // Update multiple fields
         const newDefaults = cloneDeep(defaults)
-        Object.assign(newDefaults, fieldOrFields)
+        Object.keys(fieldOrFields).forEach(key => {
+          set(newDefaults, key, get(fieldOrFields, key))
+        })
         defaults = newDefaults
       }
 
@@ -325,7 +327,7 @@ export default function useForm<TForm extends FormDataType<TForm>>(
   // Set up remember functionality
   $effect(() => {
     if (rememberKey) {
-      router.remember({ data: getData(), errors }, rememberKey)
+      router.remember({ data: formData, errors }, rememberKey)
     }
   })