flatudp: the source, kind, mock sender and stream probes

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

CMakeLists.txt

@@ -248,6 +248,8 @@ add_executable(udpscope
   src/source/e1608/e1608_kind.cpp
   src/source/e1608/e1608_panels.cpp
   src/source/flatudp/flatudp_signals.cpp
+  src/source/flatudp/flatudp_source.cpp
+  src/source/flatudp/flatudp_kind.cpp
   src/plot_host.cpp
   src/export.cpp
   src/search.cpp