docs: update TEST_SPEC.md and README.md to reflect new directory structure

- TEST_SPEC.md: Updated test directory structure to reflect Core/Asset,
  Core/IO, and Resources/<Type> subdirectories
- TEST_SPEC.md: Updated module names and test counts (852 total)
- TEST_SPEC.md: Updated build commands for new Resources subdirectories
- README.md: Updated engine structure with Core/Asset/ and Core/IO/
- README.md: Updated Resources section with layered architecture
- README.md: Updated test coverage table with accurate counts

tests/math/test_geometry.cpp

@@ -1,11 +1,11 @@
 #include <gtest/gtest.h>
-#include <XCEngine/Math/Ray.h>
-#include <XCEngine/Math/Sphere.h>
-#include <XCEngine/Math/Box.h>
-#include <XCEngine/Math/Plane.h>
-#include <XCEngine/Math/Bounds.h>
-#include <XCEngine/Math/Frustum.h>
-#include <XCEngine/Math/Matrix4.h>
+#include <XCEngine/Core/Math/Ray.h>
+#include <XCEngine/Core/Math/Sphere.h>
+#include <XCEngine/Core/Math/Box.h>
+#include <XCEngine/Core/Math/Plane.h>
+#include <XCEngine/Core/Math/Bounds.h>
+#include <XCEngine/Core/Math/Frustum.h>
+#include <XCEngine/Core/Math/Matrix4.h>
 
 using namespace XCEngine::Math;