Add a stale/never-active session reaper and raise the listen backlog

TCPServer accepted a connection and never revisited it again once it
stopped generating epoll events - a connection that completes the TCP
handshake and then goes permanently silent (an incomplete TLS
handshake, a port scanner/prober) sat in sessions forever, one
TCPSession + one fd each. sweepStaleSessions() now drops any session
that has gone 30+ seconds without a single byte of real data ever
passing through onDataReceived(), run each time a new connection
arrives rather than needing a dedicated timer. hasReceivedData latches
permanently true on a sessions first real byte, so an ordinary
connected-but-briefly-idle client is never at risk.

Also raised listen()s backlog from 20 to 128, so a burst of connection
attempts has more headroom before the kernel starts dropping SYNs.

Verified live on zephora.barant.com: a silent connection held open was
reaped within the grace window while a real concurrent connection was
left untouched, with the service remaining healthy throughout.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

TCPSocket.cpp

@@ -99,6 +99,7 @@ namespace core {
    void TCPSocket::onDataReceived(coreutils::ZString &data) {
 
       if (data.getLength() > 0) {
+	 hasReceivedData = true;
 	 lineBuffer = (char *)realloc(lineBuffer, lineBufferSize + data.getLength());
 	 memcpy(lineBuffer + lineBufferSize, data.getData(), data.getLength());
 	 lineBufferSize += data.getLength();