Documents the approach for adding per-user timezone support with
system-wide fallback. The database already stores all timestamps as
UTC via TIMESTAMPTZ columns, so the work is primarily in the display
layer: user preference storage, timezone-aware template helpers, and
UI controls for selecting a timezone.
Covers 9 phases: schema changes, sqlc queries, template utilities,
user context updates, handler changes, profile/admin UI, template
time display conversion, docker config, and testing/deployment steps.
