Take the mobile fixture's dashboard from the create call

A new dashboard is a draft, so reading it back published answers 404. The POST
already returns the document.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Uq8mtNb97A7praJLyeEYgs

frontend/tests/mobile.spec.ts

@@ -171,9 +171,8 @@ test.beforeAll(async ({ browser }) => {
     },
   })
 
-  await api(page, `/dashboards/${dashboardName}`, { method: "POST" })
   const dashboard = await (
-    await api(page, `/dashboards/${dashboardName}`)
+    await api(page, `/dashboards/${dashboardName}`, { method: "POST" })
   ).json()
   dashboard.pages[0].sections[0].widgets = [
     {