- Use code-point length instead of UTF-16 length in estimateStringChars()
so that CJK Extension B+ surrogate pairs (U+20000+) are counted as 1
character, not 2 (fixes ~25% overestimate for rare characters).
- Change long-line split step from maxChars to chunking.tokens so that
CJK lines are sliced into token-budget-sized segments instead of
char-budget-sized segments that produce ~4x oversized chunks.
- Add tests for both fixes: surrogate-pair handling and long CJK line
splitting.
Addresses review feedback from Greptile and Codex bots.
a5147d4d88