ignore SIGPIPE to prevent crash on DnD/clipboard pipe close

Wayland data transfers (drag-and-drop, clipboard) use pipes between
clients. If a client disconnects mid-transfer, writing to the pipe
raises SIGPIPE which kills the compositor. Ignore it.

src/main.c

@@ -638,6 +638,10 @@ static int real_main(int argc, char **argv)
 		sigemptyset(&ss);
 		sigaddset(&ss, SIGUSR2);
 		pthread_sigmask(SIG_BLOCK, &ss, NULL);
+
+		/* Ignore SIGPIPE — Wayland data transfers (DnD, clipboard)
+		 * can trigger broken pipes when clients disconnect. */
+		signal(SIGPIPE, SIG_IGN);
 	}
 
 	setlocale(LC_ALL, "");