ci: add clang-tidy checks to CI

[tetsuo-cpp]

Summary

• add an LLVM/MLIR-aligned clang-tidy configuration and CMake check target
• fix the existing clang-tidy findings in project sources and public headers
• standardize CI and new orb builds on Clang 20 and document the lint workflow

Validation

• cmake --build /tmp/warpforth-tidy-build
• cmake --build /tmp/warpforth-tidy-build --target check-clang-tidy
• cmake --build /tmp/warpforth-tidy-build --target check-warpforth (109/109 passed)
• cmake --build /tmp/warpforth-tidy-build --target check-format
• bash -n .agents/setup .agents/resume