Fix hard-coded macOS link directory

[be-student]

Summary

• remove the hard-coded /usr/local/lib override from the root and all example projects
• let CMake keep its compiler-detected implicit link directories on every platform

Fixes #505.

Validation

• configured with AppleClang 17 and EXAMPLES=ON
• built all six examples successfully
• full test binary: 463 passed; 6 unrelated existing fixture/parallel-coloring failures

Developed with AI assistance; I reviewed and validated the change.