warnDuplicatePreview

Emits a warning about duplicate preview ids to the platform's most discoverable warning surface. Used internally by distinctPreviewsById to surface cross-artifact same-FQN preview collisions; not part of the consumer-facing API.

Per-platform routing:

• JVM: System.err.println — keeps the warning out of stdout (where build logs are parsed by tooling) and onto the standard error stream that IDEs / CI surfaces highlight separately.

• Android: Log.w("ComposePreviewLab", ...) — picks up Logcat's warning severity filter so the line is colored / level-tagged in Android Studio.

• iOS: NSLog — routes through the unified logging system so the line shows up in Xcode console and Console.app.

• JS / Wasm JS: console.warn — yellow-highlighted in browser DevTools and surfaced separately from console.log by headless test runners that filter logs by severity.

All actuals prepend the shared WarnPrefix before message so callers and log collectors can rely on a single literal across every platform.

commonMain has no portable warning API across all CMP targets — expect/actual is the only way to route per-platform without dragging in a logging framework.