Development-signed builds now opt into the Production CloudKit
environment via com.apple.developer.icloud-container-environment,
driven by a CLOUDKIT_ENV build setting. A new Debug-CKDev configuration
and "Yattee (CloudKit Dev)" scheme switch to the Development
environment for schema work.
The DEV badge and banner in iCloud settings now reflect the actual
environment (YatteeCloudKitEnvironment Info.plist key) instead of
#if DEBUG, and the sync engine logs the environment at startup.
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