Task: B1: Extend entity SQL template to cover full table-template data shape

sql_schema_domain_entity_create.mustache, when given a domain_entity model populated with the fields added by B3, produces SQL output byte-identical to sql_schema_create.mustache for every dual-file entity. The table template is not deleted yet.

• Template renders coding_scheme_code column when domain_entity.coding_scheme is set
• Template renders image_id column when domain_entity.has_image_id is true
• Template renders the validation function body from domain_entity.validation_fn
• Template renders insert_trigger.validations rows when present
• Byte-identical SQL output verified for at least one dual-file entity (e.g. party_status)

(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.)