Standard convention: README.md at root, everything else in docs/.
Engine docs/: FFI_DESIGN, FFI_COMPLETENESS, KERNEL_BOUNDARY, NUMERICAL,
PHASE1_HISTORY, ZIGZAG_PORT. README.md links updated to docs/<name>.
Cross-repo reference in NUMERICAL.md (to topolei's STATUS.md) now
includes the relative path `../topolei/docs/STATUS.md`.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
