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>

Test/Components/DataSources/UDPStreamer/UDPStreamerTest.h

@@ -209,6 +209,31 @@ public:
      * Reassembles all fragments and verifies the total payload size.
      */
     bool TestHighFrequency_DataIntegrity();
+
+    /**
+     * @brief Tests Initialise with MulticastGroup and explicit DataPort.
+     */
+    bool TestInitialise_MulticastMode_Valid();
+
+    /**
+     * @brief Tests that DataPort defaults to Port+1 when MulticastGroup is set but DataPort is absent.
+     */
+    bool TestInitialise_MulticastMode_DefaultDataPort();
+
+    /**
+     * @brief Tests that DataPort equal to Port is rejected.
+     */
+    bool TestInitialise_MulticastMode_InvalidDataPort();
+
+    /**
+     * @brief Tests PrepareNextState in multicast mode: TCP listener opens, data socket connects.
+     */
+    bool TestPrepareNextState_Multicast();
+
+    /**
+     * @brief Tests full TCP CONNECT → CONFIG → DATA via multicast → DISCONNECT on loopback.
+     */
+    bool TestExecute_MulticastConnectDataDisconnect();
 };
 
 #endif /* UDPSTREAMERTEST_H_ */