New STATIC lib + peaks_tests (CTest), mirroring bank_model. Float samples,
per-channel (no fold); exact integer bin spans handle remainder, short
buffers, and degenerate inputs with no OOB. Bin-span math guarded against
size_t overflow for pathological binCount.
Pure dependency-free core with self-contained JSON writer/parser. Absolute
paths (incl. drive-relative) rejected at the add boundary; \uXXXX decoded to
UTF-8 with surrogate pairs; malformed input returns nullopt.