Android 13+: the system shows a UI hint "Copied to clipboard" — your app
does NOT need to display its own toast (and shouldn't, per Material 3
guidance).
iOS: copy is silent — pair with a toast for user feedback if needed.
JS / wasmJs: must be called inside a user-gesture handler; falls back to
the legacy document.execCommand("copy") path if the modern Clipboard API
is unavailable.
Linux: requires xclip (X11) or wl-copy (Wayland) on PATH; without
either, returns Result.failure(UnsupportedPlatform).