-- True-instant date contract (ADR-0001 / spec #113, ticket #114).
--
-- image_exif gains the new-contract columns alongside the untouched legacy
-- `date_taken`:
--   date_utc              — true UTC instant (unix seconds) under the new
--                           contract; NULL while the row is still on the
--                           legacy convention (drain pending).
--   camera_offset_minutes — camera local − UTC in minutes that produced
--                           date_utc (NULL for direct-UTC branches).
--   date_taken_tz_source  — why the offset is what it is:
--                           offset_tag | gps | assumed_server | utc_direct
--                           | manual.
-- user_ai_prefs gains the DST-proof display zone (IANA name); the legacy
-- tz_offset_minutes column stays frozen for rollback.

ALTER TABLE image_exif ADD COLUMN date_utc BIGINT;
ALTER TABLE image_exif ADD COLUMN camera_offset_minutes INTEGER;
ALTER TABLE image_exif ADD COLUMN date_taken_tz_source TEXT;
ALTER TABLE user_ai_prefs ADD COLUMN display_tz TEXT;