Add stratified_v6 train split (canonicalized spelling/ZWJ/register/typo fixes)

Add stratified_v6 validation split (canonicalized spelling/ZWJ/register/typo fixes)

Add stratified_v6 test split (canonicalized spelling/ZWJ/register/typo fixes)

Add stratified_v5: register-spelling and word-boundary/ZWJ conjunct normalization applied on top of stratified_v4 (407 register pairs, 60 boundary pairs; 13,120 of 154,828 rows changed). Text-only changes, audio bytes unchanged from v4.

Patch 1 row: rule that failed to apply in first batch pass

Patch 8 rows: rules that failed to apply in first batch pass

Move stratified_v4 under data/