Task 1 of the IBKR UCITS volume source plan: adds ibkr_pit_volume (first-seen-
frozen, mirrors yahoo_pit_volume), IbkrBroker.historical_daily_volume
(reqHistoricalData TRADES, integration-only, never raises), and the
ucits_volume_source config flag (default yahoo, additive ibkr path). Task 2
(CLI + provider read) and Task 3 (CronJob) are separate follow-ons.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>