Story: Finish integrating calendar reference data: XML export and DQ publish

Split from Sprint 23's Model calendars as proper ORE Studio reference data at close: that story shipped the calendar domain model, the FK relationships from currency/currency_pair_convention, the Qt CRUD screens, and the currency_country junction (5/7 of its own acceptance). Two integration items remain, both about making the new calendar model actually reachable by the rest of the system rather than just existing in the database:

1. ores.ore's conventions_mapper (or successor) should build ORE's comma-joined calendar-name string from the FK relationship(s) only at the XML export boundary — the domain model itself never stores the joined string.
2. currency_country and currency_calendar (and currency_pair_convention_calendar) need wiring into the DQ bundle publication pipeline — calendar=/=calendar_type already have this from the entity task.

• ores.ore's conventions_mapper builds ORE's comma-joined calendar-name string only at the XML export boundary, from the FK relationship(s); the domain model itself never stores the joined string.
• currency_country, currency_calendar, and currency_pair_convention_calendar are published through the DQ bundle pipeline (artefact tables + publish-from-dq functions + NATS handlers).

• currency_calendar and currency_pair_convention_calendar turned out to already be fully DQ-publish-wired, delivered early alongside the calendar=/=calendar_type pipeline (0a167d548 [sql/dq] Add DQ publish pipeline for calendars and calendar types) — only currency_country had a real gap by the time the DQ-publish task started.
• currency_country's DQ artefact seed script copies the live ores_refdata_currency_countries_tbl verbatim rather than deriving it, unlike currency_calendars (which derives calendar assignments from country matches) — currency_country itself is the source of truth, not something computed from other data.

• Everything already shipped by the parent story (entity model, FK relationships, Qt screens, currency_country junction) — see Model calendars as proper ORE Studio reference data.
• The three extras (holiday-aware date picker, list-pagination fix, QuantLib materialization) — already split off separately into Calendar entity follow-ups in the product backlog.