ProxyLinkWarningListener

Re-surfaces the ProxyLinkWarning to operators as they connect, so the "proxy is missing RSPM" diagnosis never depends on someone having read the one-shot startup console. Also detects the proxy-only-Floodgate topology — no Bedrock plugin on the backend at all — the moment a Bedrock player arrives through the proxy, which is the only backend-observable signal that this is a Bedrock network.