Migrated from Make to CMake.

docs/IDEA.md

@@ -172,7 +172,7 @@ Adapt this to an existing repository instead of replacing it blindly.
 xtc/
 ├── README.md
 ├── LICENSE
-├── Makefile
+├── CMakeLists.txt
 ├── docs/
 │   ├── ARCHITECTURE.md
 │   ├── AUDIO_ENGINE.md
@@ -624,8 +624,8 @@ make an edit partially visible if it fails validation.
 
 ### Build system
 
-Use a straightforward Makefile unless the existing repository has a sound reason
-to use another build system.
+Use the root CMake project and CTest. Keep SDK integrations optional and
+all generated output in separate build directories.
 
 The build must:
 
@@ -736,7 +736,7 @@ feature is exciting.
 ### Repository and design baseline
 
 - Inspect the repository and available toolchain.
-- Create or update architecture documentation and the Makefile.
+- Create or update architecture documentation and the CMake project.
 - Verify C compiler, C++ compiler, FLTK, audio development headers, and test
   tools.
 - Record dependency and licensing decisions.
@@ -851,7 +851,7 @@ Start with the **repository and design baseline** only.
    development packages, `pkg-config`, and test tools.
 3. Do not install packages or modify system configuration without permission.
 4. Propose the smallest initial source tree compatible with this brief.
-5. Add or update the Makefile and documentation only as needed.
+5. Add or update the CMake project and documentation only as needed.
 6. Create a minimal program that builds and exits cleanly; do not yet implement
    a full audio engine or GUI.
 7. Build it and run its tests.