Add a new entity across all layers

Add a new domain entity (e.g. currency, counterparty, trade) with support across all layers: domain type, SQL schema, repository, service, Qt UI, CLI commands, HTTP endpoints, and unit tests.

• Entity name and fields are defined.
• Current sprint has a story for this entity.
• Build environment is configured per development environment setup.

In execution order:

1. Create the domain type. Use Domain Type Creator skill to generate the C++ domain model, serialisation, and JSON I/O.
2. Create the SQL schema. Use SQL entity schema patterns and How do I create entity schema? to add the table, CRUD functions, and grants.
3. Create the repository. Follow Entity lifecycle to scaffold the C++ repository class.
4. Wire the service layer. Add NATS handlers and service methods following the protocol conventions in Protocol Reference.
5. Create the Qt UI. Follow Qt entity patterns: ClientModel → list window → detail dialog → history dialog. Use How do I create entity UI?.
6. Add CLI commands. Follow CLI entity patterns and How do I create entity commands? (CLI).
7. Add HTTP endpoints. Follow Shell entity patterns and How do I create entity endpoints?.
8. Write unit tests. Follow Unit test conventions and Unit Test Writer skill.
9. Commit and PR. Follow Work a task through to merged PR for the full PR lifecycle.

• Entity is functional across all layers.
• All tests pass.
• RLS policies (tenant isolation; party isolation if party_id present) are in place and registered in rls/rls_create.sql.
• Detail dialog calls promptChangeReason() before save (Create/Amend) and before delete; change_reason_code and change_commentary are set on the domain entity before the request is sent.
• Notify trigger uses ores_utility_iso8601_timestamp_fn(change_timestamp) for the timestamp field in pg_notify payloads.
• PR is open with the entity changes.

• Entity lifecycle — layer ordering and type mappings.
• Work a task through to merged PR — the PR lifecycle runbook.
• Runbooks catalogue — all runbooks.