Task: Migrate content: move _table.org sections into entity files and delete table files

All 11 _table.org files are deleted; their SQL sections live in the corresponding entity files and regenerate identical output.

• All 9 dual-file entities have * Validation function and * Insert trigger sections in their entity org files.
• Generated SQL for each migrated entity is byte-identical to what the table pathway previously produced.
• All 11 _table.org files are deleted from projects/ores.refdata/modeling/.
• purpose_type entity file has #+sql_only: true and generates correct SQL; currency_table.org is deleted once commission-currency sync tasks complete.

(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.)