tests: add Common placeholder smoke/gtest tests and MockCoordTrans

Lts/Common/CommonUnitTestsPlaceholder/mocks/CMakeLists.txt

@@ -0,0 +1,5 @@
+add_library(MockCoordTrans STATIC MockCoordTrans.h)
+target_include_directories(MockCoordTrans PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+
+# Export header-only semantics by providing an interface target
+add_library(MockCoordTrans::MockCoordTrans ALIAS MockCoordTrans)

Lts/Common/CommonUnitTestsPlaceholder/mocks/MockCoordTrans.h

@@ -0,0 +1,16 @@
+#pragma once
+#include <utility>
+
+// Minimal realistic mock for coordinate transforms used during migration.
+// Forward conversion returns approximate meters using lat/lon*111000.
+class MockCoordTrans {
+public:
+  // approximate forward: (lat, lon) -> (x_m, y_m)
+  static std::pair<double,double> forward(double lat_deg, double lon_deg) {
+    return {lat_deg * 111000.0, lon_deg * 111000.0};
+  }
+  // approximate inverse
+  static std::pair<double,double> inverse(double x_m, double y_m) {
+    return {x_m / 111000.0, y_m / 111000.0};
+  }
+};