refactor: simplify D3D12 test infrastructure

- Delete run_tests.py and run_tests.bat (use cmake/ctest directly)
- Fix integration test CMakeLists: output_ppm name, threshold=0, GT.ppm copy
- Rewrite TEST_SPEC.md to be concise
- Update integration test CTest registration

tests/RHI/D3D12/integration/minimal/CMakeLists.txt

@@ -46,6 +46,6 @@ add_test(NAME D3D12_Minimal_Integration
         $<TARGET_FILE:D3D12_Minimal>
         minimal.ppm
         ${CMAKE_CURRENT_SOURCE_DIR}/GT.ppm
-        5
+        0
     WORKING_DIRECTORY $<TARGET_FILE_DIR:D3D12_Minimal>
 )

tests/RHI/D3D12/integration/quad/CMakeLists.txt

@@ -55,6 +55,6 @@ add_test(NAME D3D12_Quad_Integration
         $<TARGET_FILE:D3D12_Quad>
         quad.ppm
         ${CMAKE_CURRENT_SOURCE_DIR}/GT.ppm
-        5
+        0
     WORKING_DIRECTORY $<TARGET_FILE_DIR:D3D12_Quad>
 )

tests/RHI/D3D12/integration/sphere/CMakeLists.txt

@@ -43,13 +43,16 @@ add_custom_command(TARGET D3D12_Sphere POST_BUILD
     COMMAND ${CMAKE_COMMAND} -E copy_if_different
         ${CMAKE_SOURCE_DIR}/tests/RHI/D3D12/integration/run_integration_test.py
         $<TARGET_FILE_DIR:D3D12_Sphere>/
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different
+        ${CMAKE_CURRENT_SOURCE_DIR}/GT.ppm
+        $<TARGET_FILE_DIR:D3D12_Sphere>/
 )
 
 add_test(NAME D3D12_Sphere_Integration
     COMMAND ${Python3_EXECUTABLE} $<TARGET_FILE_DIR:D3D12_Sphere>/run_integration_test.py
         $<TARGET_FILE:D3D12_Sphere>
-        screenshot.ppm
+        sphere.ppm
         ${CMAKE_CURRENT_SOURCE_DIR}/GT.ppm
-        5
+        0
     WORKING_DIRECTORY $<TARGET_FILE_DIR:D3D12_Sphere>
 )

tests/RHI/D3D12/integration/triangle/CMakeLists.txt

@@ -52,6 +52,6 @@ add_test(NAME D3D12_Triangle_Integration
         $<TARGET_FILE:D3D12_Triangle>
         triangle.ppm
         ${CMAKE_CURRENT_SOURCE_DIR}/GT.ppm
-        5
+        0
     WORKING_DIRECTORY $<TARGET_FILE_DIR:D3D12_Triangle>
 )