Firebase App Check Manager

⚠️ #1 ROOT CAUSE of "App attestation failed": Missing Team ID or API not enabled

Two things MUST be in place for iOS App Check to work:

1. firebaseappcheck.googleapis.com API must be ENABLED — even if you've configured providers in Console, if this API isn't enabled, all token exchanges fail silently.
2. iOS App must have teamId set — Without Team ID, App Attest cannot verify with Apple's servers.

Team ID can be set via REST API (no Console UI needed):

curl -X PATCH -H "Authorization: Bearer $ACCESS_TOKEN" \
  -H "x-goog-user-project: ${PROJECT_ID}" \
  -H "Content-Type: application/json" \
  -d '{"teamId":"YOUR_TEAM_ID"}' \
  "https://firebase.googleapis.com/v1beta1/projects/${PROJECT_ID}/iosApps/${IOS_APP_ID}?updateMask=teamId"

If Team ID is already set and API is enabled, verify app registration through Firebase Console → App Check → 應用程式 tab. Required IAM role: roles/editor or roles/owner (not just roles/firebase.viewer or roles/firebaseappcheck.admin).