Fix MSW test helper to clone request before reading body

Clone the request before calling .json() to prevent "Request already used"
errors in MSW handlers.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jkebinger

test/test-helper.ts

@@ -105,7 +105,7 @@ export const getCannedResponse = async (
   let body: DefaultBodyType = {}
 
   if (request.method === 'POST') {
-    body = await request.json()
+    body = await request.clone().json()
 
     if (!body || typeof body !== 'object') {
       throw new Error('Expected http body to be an object')