Fail a download whose file server stops sending

The data socket had no read timeout, so a file server that went quiet
left the transfer, and its thread, waiting until the user cancelled.
Thirty seconds without data now fails it.

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

ts3-client/core/src/main/java/com/ts3client/net/filetransfer/FileTransferManager.java

@@ -46,6 +46,8 @@ import java.util.function.Supplier;
 public final class FileTransferManager {
 
     private static final int CONNECT_TIMEOUT_MS = 15_000;
+    /** How long a download may go without receiving anything before it counts as failed. */
+    private static final int STALL_TIMEOUT_MS = 30_000;
     private static final int BUFFER_SIZE = 64 * 1024;
     /** How long to wait for the server's {@code notifystart*} reply after an {@code ftinit*}. */
     private static final long NEGOTIATE_TIMEOUT_MS = 15_000;
@@ -406,6 +408,7 @@ public final class FileTransferManager {
         Socket socket = new Socket();
         socket.connect(new InetSocketAddress(resolveHost(params.getFileServerHost()),
                 params.getFileServerPort()), CONNECT_TIMEOUT_MS);
+        socket.setSoTimeout(STALL_TIMEOUT_MS);
         return socket;
     }