-- Per-user display timezone: a *presentation* preference only.
--
-- Every timestamp in this system is and stays UTC -- ingest records
-- Unix nanoseconds, ClickHouse stores DateTime64 in UTC, and both the
-- query API and every JSON response continue to emit RFC3339 with a Z
-- offset. This column changes nothing about any of that. It only tells
-- the web UI which offset to render those instants in, so two users in
-- two timezones looking at the same log line see the same instant
-- written two different ways, never two different log lines.
--
-- Stored as an IANA zone name ('UTC', 'America/New_York', ...) rather
-- than a fixed numeric offset, because a fixed offset is wrong twice a
-- year for anywhere that observes DST -- the zone name is what carries
-- the rule, not just today's answer. Validated in Go against the
-- embedded tzdata (see api/localauth's handleSetTimezone) rather than
-- by a CHECK constraint: the valid set is the tz database's, which
-- Postgres would have no way to keep in sync here.
--
-- Default 'UTC' matches the "standardize on UTC" baseline -- a user who
-- never touches this setting sees exactly what they saw before it
-- existed.
ALTER TABLE users
    ADD COLUMN IF NOT EXISTS display_timezone TEXT NOT NULL DEFAULT 'UTC';