Firewall hangs or crashes Jamlus

## Describe the bug

Clicking Connect while Ethernet is active and the macOS Application Firewall is enabled causes either an immediate crash (SIGPIPE, exit code 141) or a permanent hang. WiFi is not affected.

## To Reproduce

1. Plug in Ethernet (both Ethernet and WiFi active, default route via `en0`)
2. Enable the macOS Application Firewall via gui: or probably `sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate on`
3. Launch Jamulus and click Connect
4. The app either crashes immediately or hangs with no response from the server

**Workaround:** Unplug Ethernet, disable the firewall, or add Jamulus to the firewall allow list.

## Expected behavior

Connect works regardless of which network interface is used and whether the firewall is enabled. If the server is unreachable, show an error instead of crashing or hanging.

## Crash report (before fix)

```
frame #0: __sendto (libsystem_kernel.dylib)
frame #1: Jamulus CSocket::Send (socket.cpp)
frame #2: Jamulus (ConnLessProtocol / Protocol layer)
frame #3: Jamulus (Protocol layer)
frame #4: QtCore QSocketNotifier (via Qt event loop)
frame #5-8: Jamulus (various)
frame #9: QObject::event
frame #10: QWidget::event
frame #11-12: QtWidgets QApplication
frame #13: QtCore QCoreApplication::sendEvent
frame #14: QtCore QCoreApplicationPrivate::sendPostedEvents
```

## Root cause (likely; AI assisted)

The macOS Application Firewall silently drops Jamulus's outgoing UDP packets when traffic originates from the Ethernet interface. WiFi works because it was already trusted (?). Before the fix, the dropped packets caused a SIGPIPE (no receiver). After the SO_NOSIGPIPE fix (handling macOS like iOS), it became a hang since the connection attempt never completes and `IsConnected()` stays false.

## Operating system

macOS 26.5.2, Apple Silicon (arm64), Xcode 26.6

## AI proposed Fix

Two changes were needed of which the first one I am not sure about:

**1. SO_NOSIGPIPE** (`src/socket.cpp`):

```cpp
// Before:
#ifdef Q_OS_IOS
int valueone = 1;
setsockopt ( UdpSocket, SOL_SOCKET, SO_NOSIGPIPE, &valueone, sizeof ( valueone ) );
#endif

// After:
#if defined( Q_OS_IOS ) || defined( Q_OS_MACOS )
int valueone = 1;
setsockopt ( UdpSocket, SOL_SOCKET, SO_NOSIGPIPE, &valueone, sizeof ( valueone ) );
#endif
```

This prevents a SIGPIPE crash but doesn't fix the hang.

**2. Connection timeout** (`src/clientdlg.cpp`):

Added a 5-second `TimerConnectTimeout` in `CClientDlg`. If `IsConnected()` is still false when it fires, the app shows a warning about the firewall and disconnects. The timer is stopped on successful connection (`OnConClientListMesReceived`) or on manual disconnect.

To be discussed.
## Additional context

/

Comienza con la ruta del fallo en src/socket.cpp, especialmente con CSocket::Send; después inspecciona el flujo de conexión y las ubicaciones de timeout propuestas en src/clientdlg.cpp y CClientDlg. Reproduce el caso de Ethernet más firewall si es posible; se considera terminado cuando los intentos de conexión ya no provocan fallos ni se quedan bloqueados y un servidor inaccesible produce el comportamiento descrito de advertencia y desconexión.

Escrito por el modelo de indexación a partir del texto del issue.