refactor: Modularize CMake build system into 10 specialized modules

Refactor monolithic 866-line CMakeLists.txt into 54-line orchestrator + 10 modules:
- DemoOptions.cmake - Build option declarations
- DemoConfig.cmake - Option implications and platform detection
- DemoCommon.cmake - Shared macros (conditional sources, size opts, linking)
- DemoDependencies.cmake - External library discovery (WGPU, GLFW)
- DemoSourceLists.cmake - Conditional source file lists
- DemoLibraries.cmake - Subsystem library targets
- DemoTools.cmake - Build tools (asset_packer, compilers)
- DemoCodegen.cmake - Code generation (assets, timeline, music)
- DemoExecutables.cmake - Main binaries (demo64k, test_demo)
- DemoTests.cmake - Test infrastructure (36 tests)
- Validation.cmake - Uniform buffer validation

Benefits:
- 94% reduction in main file size (866 → 54 lines)
- Conditional module inclusion (tests only parsed if DEMO_BUILD_TESTS=ON)
- Shared macros eliminate 200+ lines of repetition
- Clear separation of concerns

All 36 tests passing. All build modes verified.

Documentation: Created doc/CMAKE_MODULES.md with module architecture.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/cmake/DemoLibraries.cmake b/cmake/DemoLibraries.cmake
new file mode 100644
index 0000000..3a2207a
--- /dev/null
+++ b/cmake/DemoLibraries.cmake
@@ -0,0 +1,30 @@
+# Subsystem Library Targets
+# Defines the 5 core static libraries
+
+# Utility library
+add_library(util STATIC ${UTIL_SOURCES})
+add_dependencies(util generate_demo_assets generate_test_assets)
+target_include_directories(util PUBLIC ${CORE_INCLUDES})
+
+# Procedural generation library
+add_library(procedural STATIC ${PROCEDURAL_SOURCES})
+target_include_directories(procedural PUBLIC ${CORE_INCLUDES})
+
+# Audio synthesis and processing library
+add_library(audio STATIC ${AUDIO_SOURCES})
+add_dependencies(audio generate_demo_assets)
+target_include_directories(audio PUBLIC ${CORE_INCLUDES})
+
+# 3D rendering library
+add_library(3d STATIC ${3D_SOURCES})
+add_dependencies(3d generate_demo_assets)
+target_include_directories(3d PUBLIC ${CORE_INCLUDES})
+
+# GPU effects library
+add_library(gpu STATIC ${GPU_SOURCES})
+add_dependencies(gpu generate_demo_assets)
+target_include_directories(gpu PUBLIC ${CORE_INCLUDES})
+
+# Note: Static libraries do not strictly need to link dependencies,
+# but if they did, PRIVATE would propagate to the executable.
+# We will link them in the executable to be explicit and avoid order issues.