Task: As-of window-join read-side composition query

Add a read-side query so a caller can fetch a parent entity as it stood at a specific version, and its children filtered to that same version's [valid_from, valid_to) window — reaching all the way to the repository and service layers, codegen-driven for any future entity.

• Any versioned entity gets a generic read_at_version=/=get_<entity>_at_version repository+service method (gated on has_audit_columns, not a new opt-in flag — genuinely applies to every entity, per the author's direction).
• Any child FK opted into :list_by_as_of: true gets a read_by_<fk>_as_of=/=list_<entity>_by_<fk>_as_of repository+service method doing the interval-overlap query against a caller-supplied window.
• Codegen-driven for counterparty; hand-patched to match for party (2 of its 3 entities use an older, pre-generic-facet hand-written repository/service shape — patched to match their own existing conventions rather than pulled onto the modern shape, which is a separate, larger modernization out of scope here).
• Proven with a new repository test (as_of_composition_reflects_party_version_history) exercising the full mechanism against a real party+identifier; full party/counterparty test suite (28 test cases, 47 assertions) passes.
• NATS messaging/protocol layer deliberately deferred to the Qt composite history dialog task, which needs it anyway.

Extended the FK-flag mechanism from the touch-function task with a mirror pair: :list_by_as_of: (child FK, read side) alongside :bump_parent_version: (child FK, write side), and made read_at_version=/=get_<entity>_at_version unconditional for any has_audit_columns entity rather than a new flag, since a single-entity as-of fetch is useful standalone, not just for composite parents.

Regenerated counterparty's repository+service layers via compass codegen regenerate --component refdata-cpp --profile repository|service, then manually scoped the diff to only the entities actually touched — the regen run picks up large amounts of unrelated pre-existing drift across ~20+ other refdata entities each time (a known, separate gap — some entities are stuck on an older hand-written shape: constructor-held context, boost::uuids::uuid params instead of std::string=+per-call =context). Reverted those; not this task's concern.

counterparty_contact_information and party_identifier's sibling party_contact_information (plus party itself) are on that older shape — regenerating them wholesale would have required also updating their service/handler/test layers to the modern interface, well beyond this task. Hand-patched the 2 new methods into each file matching its own existing convention (context-in-constructor, boost::uuids::uuid params) rather than the modern generated shape, exactly as done for party's SQL in the touch-function task.

domain::party (and siblings) only surface recorded_at (= valid_from), not valid_to, on the domain struct — discovered while writing the proof test. Windows are contiguous by construction (closing one version's valid_to is the next version's valid_from), so the test derives v1's window end from v2's recorded_at rather than needing a valid_to field; the still-open latest version's open end is bounded with a safely-far-future instant instead of the real infinity sentinel (domain objects don't carry that either).

Landed and proven: read_at_version=/=get_<entity>_at_version for any versioned entity, read_by_<fk>_as_of=/=list_<entity>_by_<fk>_as_of for any :list_by_as_of:-opted-in child FK, reaching repository and service layers. Codegen-driven for counterparty; hand-patched to match party's (and 2 other stale entities') existing conventions. NATS/protocol layer deferred to the Qt composite history dialog task. New test proves the composition end-to-end against real data; full party/counterparty suite (28 cases, 47 assertions) passes.