Task: Unify the SQL template to support validation function and insert trigger from entity models

Running –profile sql on an ores.codegen.entity model produces byte-identical output to the current table-pathway for the same entity, including the validation function body and insert trigger.

• sql_schema_domain_entity_create.mustache generates a validation function body from entity model data.
• Insert trigger FK validations are rendered from entity model data.
• Output is byte-identical to the existing table-pathway SQL for at least one migrated entity (e.g. rounding_type).

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)