Fix getById not returning USB policy fields

The getByIdHandler was missing usbPolicy, usbPolicyStatus,
and usbPolicyError fields, causing the chip to always show
"Permitido" instead of the actual policy value.

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

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

convex/machines.ts

@@ -1143,6 +1143,9 @@ export async function getByIdHandler(
     lastPostureAt,
     remoteAccess: machine.remoteAccess ?? null,
     customFields: machine.customFields ?? [],
+    usbPolicy: machine.usbPolicy ?? null,
+    usbPolicyStatus: machine.usbPolicyStatus ?? null,
+    usbPolicyError: machine.usbPolicyError ?? null,
   }
 }