Fix Zod schema type mismatch with zodResolver

Remove .default() from schema fields — zodResolver uses Zod input
types where .default() makes fields optional. Defaults are already
provided via useForm defaultValues.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jonradoff

frontend/src/pages/admin/AnnouncementsPage.tsx

@@ -150,8 +150,8 @@ export default function AnnouncementsPage() {
 
 const announcementSchema = z.object({
   title: z.string().trim().min(1, 'Title is required'),
-  body: z.string().trim().default(''),
-  publish: z.boolean().default(false),
+  body: z.string().trim(),
+  publish: z.boolean(),
 });
 
 type AnnouncementFormData = z.infer<typeof announcementSchema>;