feat(core): Gnutella joining after Java, measured against Java

GnutellaRun lets Java's PeerToPeerAnwendung join peers on terminal-net.
The core's gnutella.ts does the same: a ping in Java's text format to
port 6346, a pong back, the ping sent on to the other peers and their
pongs back the way it came, at most the program's number of peers.

Departure from Java: a ping that comes a second time gets no pong and
its connection stays (Java's worker throws on the missing pong).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/test/javaRun.ts

@@ -63,7 +63,7 @@ export interface SeenFrame {
   readonly text: string;
 }
 
-function javaText(frame: JavaFrame): string {
+export function javaText(frame: JavaFrame): string {
   const macs = `${frame.source} > ${frame.destination}`.toUpperCase();
   if (frame.arp !== undefined) return `${macs} ARP ${frame.arp === 1 ? 'request' : 'reply'} ${frame.senderIp} > ${frame.targetIp}`;
   if (frame.icmp !== undefined) return icmpText(macs, frame.icmp, frame.icmpCode!, frame.sourceIp!, frame.destinationIp!, frame.sequence!);