getBedrockSeenBehindUnlinkedProxy

True once a Bedrock player has been observed connecting while this backend was proxied but unkeyed — the proxy-only-Floodgate case, where nothing on the backend's filesystem reveals that Bedrock is in play. Persisted so the boot warning fires on later restarts too, before any Bedrock player has reconnected. Self-clears: the warning is gated on the unkeyed state, so a successful link silences it regardless of this flag.