Replace the NSSpellChecker + regex-stub engine with harper-core 2.5.0:
real subject-verb agreement, verb forms, punctuation, repetition and
spelling. New harper-ffi crate (staticlib) exposes harper_check over a C
ABI; the CHarper module bridges it to Swift; HarperEngine maps Harper's
char spans onto UTF-16 ranges and de-dups overlapping lints. NSSpellChecker
stays only as a case-preserving spelling supplement, which fixes the
problemm->Problem mis-casing. Bulk apply now skips no-op suggestions.
build.sh / scripts/build.sh build the universal static lib; target/ and
lib/ are gitignored (regenerate via harper-ffi/build.sh).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
