docs: record the CMake build-system split in COMPLETED; note the multi-config ctest flag

CLAUDE.md

@@ -42,6 +42,10 @@ Vendors three submodules (see `.gitmodules`):
     cmake --build build
     ctest --test-dir build
 
+On a multi-config generator (Visual Studio, Xcode) the bare `ctest` command above
+reports every test as "Not Run" — add `-C Debug` (or whichever config was built) to
+resolve the test executables. Single-config generators (Ninja, Make) need no such flag.
+
 Every pure module has a corresponding `<module>_tests` executable target that runs without REAPER or a DAW. Targets are declared per directory: each `src/**/CMakeLists.txt` owns its own libraries and their test targets, added via `add_subdirectory` from the root, which keeps only repo-global settings (version, channel, vendor paths). `cmake/reasampler_targets.cmake` holds the two shared declaration helpers. The two loadable-module targets are `reaper_reasampler` (the REAPER extension `.dll`/`.dylib`/`.so`) and `reasampler_vst` (the VST3 instrument; Windows-only, omitted if the `vendor/vst3sdk` slice is absent). The `sample_usage_tests` executable target runs the pure unit tests for `sample_usage` (no REAPER, no DAW).
 
 ### Beta channel build