Add TCP control + UDP multicast mode to UDPStreamer

DataSource (C++):
- New optional config: MulticastGroup (e.g. "239.0.0.1") and DataPort
  (default Port+1); when set, enables multicast mode; absent = unicast
- Control plane: BasicTCPSocket listener on Port; CONNECT received over
  TCP triggers HandleTCPConnect() which sends CONFIG via the same TCP
  connection
- Data plane: BasicUDPSocket aimed at MulticastGroup:DataPort; all DATA
  fragments sent via dataSocket.Write() so any joined client receives them
- useMulticast is the single branch point; every unicast code path is
  unchanged when MulticastGroup is absent
- New methods: HandleTCPConnect(), IsMulticast()
- 5 new unit tests (ports 44710-44729); all 38 tests passing

WebUI hub (Go):
- SourceConfig gains MulticastGroup and DataPort fields (JSON, optional)
- UDPClient gains multicastGroup/dataPort; Run() routes to new
  runMulticastSession() when multicastGroup is non-empty
- runMulticastSession(): TCP dial for CONNECT/CONFIG, net.ListenMulticastUDP
  for DATA, background goroutine watches TCP for DISCONNECT/close
- All existing sm.Add() call sites updated (unicast callers pass "", 0)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Source/Components/DataSources/UDPStreamer/UDPStreamer.h

@@ -31,6 +31,7 @@
 /*---------------------------------------------------------------------------*/
 /*                        Project header includes                            */
 /*---------------------------------------------------------------------------*/
+#include "BasicTCPSocket.h"
 #include "BasicUDPSocket.h"
 #include "CompilerTypes.h"
 #include "EmbeddedServiceMethodBinderI.h"
@@ -275,6 +276,11 @@ public:
      */
     bool IsClientConnected() const;
 
+    /**
+     * @brief Returns true when multicast mode is active (MulticastGroup was set in config).
+     */
+    bool IsMulticast() const;
+
 private:
     /**
      * @brief Serializes the CONFIG payload into buf and sets payloadSize.
@@ -296,10 +302,16 @@ private:
     bool SendFragmented(uint8 type, uint32 counter, const uint8 *payload, uint32 payloadSize);
 
     /**
-     * @brief Handles a single received command packet from a client.
+     * @brief Handles a single received command packet from a client (unicast mode).
      */
     void HandleClientCommand(const uint8 *buf, uint32 size);
 
+    /**
+     * @brief Handles a CONNECT received on the TCP control socket (multicast mode).
+     * @details Validates magic+type, sets clientConnected, builds and sends CONFIG via tcpClient.
+     */
+    void HandleTCPConnect(const uint8 *buf, uint32 size);
+
     /**
      * @brief Maps a MARTe2 TypeDescriptor to the UDPS_TYPECODE_* constants.
      */
@@ -330,11 +342,19 @@ private:
     uint8  *wireBuffer;      /**< Pre-allocated buffer for the serialized DATA payload */
     uint32  totalWireBytes;  /**< Total bytes of all signals after quantization + 8-byte timestamp prefix */
 
-    /* Networking */
-    BasicUDPSocket  serverSocket;    /**< Bound to port; receives client commands */
-    BasicUDPSocket  clientSocket;    /**< Configured to send to the connected client */
+    /* Networking — unicast mode */
+    BasicUDPSocket  serverSocket;    /**< Bound to port; receives client commands (unicast) */
+    BasicUDPSocket  clientSocket;    /**< Configured to send to the connected client (unicast) */
     volatile bool   clientConnected; /**< True when a client has successfully connected */
 
+    /* Networking — multicast mode (only used when useMulticast == true) */
+    StreamString    multicastGroup;  /**< Multicast group IP, e.g. "239.0.0.1"; empty = unicast */
+    uint16          dataPort;        /**< UDP port for DATA datagrams in multicast mode */
+    bool            useMulticast;    /**< Derived from multicastGroup.Size() > 0 in Initialise() */
+    BasicTCPSocket  tcpListener;     /**< TCP server socket: accepts control connections */
+    BasicTCPSocket *tcpClient;       /**< Accepted TCP control connection (heap by WaitConnection) */
+    BasicUDPSocket  dataSocket;      /**< UDP socket aimed at multicastGroup:dataPort */
+
     /* Thread management */
     SingleThreadService executor;    /**< Background thread service */