Add Coverage.cmake with gcovr integration, detecting Clang vs
GCC and wrapping llvm-cov gcov in a build-dir script to handle
paths with spaces on Windows. Update README and AGENTS.md with
the new one-command-per-block documentation rule.
Enable UNITY_OUTPUT_COLOR and UNITY_INCLUDE_PRINT_FORMATTED via
compile definitions on the unity target so colors propagate to all
test suites automatically.
Add a 'check' custom target that builds all suites and runs CTest
with --output-on-failure and USES_TERMINAL, keeping ANSI colors
alive through Ninja's buffering.
portersky