ui: compact cursor and measurement readouts at the top of the dock

Both views are written from the same variable at the same call site, so the dock cannot disagree with the full panels.

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

CMakeLists.txt

@@ -269,6 +269,7 @@ add_executable(udpscope
   src/ui_status.cpp
   src/ui_measure.cpp
   src/ui_cursors.cpp
+  src/ui_dock.cpp
   src/ui_math.cpp
   src/ui_layout.cpp
   src/ui_source.cpp