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/UDPStreamerGTest.cpp

@@ -200,3 +200,28 @@ TEST(UDPStreamerGTest, TestHighFrequency_DataIntegrity) {
     UDPStreamerTest test;
     ASSERT_TRUE(test.TestHighFrequency_DataIntegrity());
 }
+
+TEST(UDPStreamerGTest, TestInitialise_MulticastMode_Valid) {
+    UDPStreamerTest test;
+    ASSERT_TRUE(test.TestInitialise_MulticastMode_Valid());
+}
+
+TEST(UDPStreamerGTest, TestInitialise_MulticastMode_DefaultDataPort) {
+    UDPStreamerTest test;
+    ASSERT_TRUE(test.TestInitialise_MulticastMode_DefaultDataPort());
+}
+
+TEST(UDPStreamerGTest, TestInitialise_MulticastMode_InvalidDataPort) {
+    UDPStreamerTest test;
+    ASSERT_TRUE(test.TestInitialise_MulticastMode_InvalidDataPort());
+}
+
+TEST(UDPStreamerGTest, TestPrepareNextState_Multicast) {
+    UDPStreamerTest test;
+    ASSERT_TRUE(test.TestPrepareNextState_Multicast());
+}
+
+TEST(UDPStreamerGTest, TestExecute_MulticastConnectDataDisconnect) {
+    UDPStreamerTest test;
+    ASSERT_TRUE(test.TestExecute_MulticastConnectDataDisconnect());
+}