Fix: Use optional() instead of default() for limit parameter

- Fixes TypeScript type incompatibility with ZodDefault
- limit is now optional number instead of defaulted
- Handle default value in code instead of schema

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/tools/builtin/messaging.ts

@@ -20,7 +20,7 @@ const SendMessageSchema = z.object({
 });
 
 const ReceiveMessagesSchema = z.object({
-  limit: z.number().default(10),
+  limit: z.number().optional(),
 });
 
 type SendMessageInput = z.infer<typeof SendMessageSchema>;