`Package.swift` but `defaultDebugLogger()` used Apple's modern
`Logger` API, which is iOS 14 / macOS 11 / tvOS 14 / watchOS 7+.
Apps with a deployment target below those minimums failed to compile
the SDK with `'Logger' is only available in iOS 14.0 or newer`.
- `defaultDebugLogger()` now branches on availability. iOS 14+ uses
`Logger` with structured `privacy: .public` interpolation; older
OS versions fall back to the legacy `os_log` family (iOS 10+).
Signal vocabulary identical; Console.app filtering on the
`com.crossdeck.sdk` subsystem works on both paths.
- Package now compiles against any deployment target ≥ iOS 13 —
same floor `Package.swift` has always claimed.
- No API changes. Strictly additive availability gate.