fix(api): clear sniff deadline before entering Redis handler

Clear the 10s read deadline before calling handleRedisConnection so
that authenticated Redis clients are not disconnected by an i/o timeout
after 10 seconds of idle time. HTTP paths already clear the deadline
after routing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/api/protocol_multiplexer.go

@@ -115,6 +115,7 @@ func (s *Server) routeMuxConnection(conn net.Conn, httpListener *muxListener) {
 			}
 			return
 		}
+		_ = conn.SetReadDeadline(time.Time{})
 		s.handleRedisConnection(conn, reader)
 		return
 	}