[SiteRelEnby]

Adds the display-timezone preference to Android, mirroring web's two tiers.

Tiers

• Account default (System.timezone): an IANA zone or null = "Automatic" (each device's own clock). Synced across devices and exported. Set via PATCH /v1/systems/me.
  • "Automatic" is an explicit null the server must receive. Since Moshi codegen drops null fields and the backend uses model_dump(exclude_unset=True) (omit = unchanged, null = auto), the account tier sends a dedicated single-field body serialized with .serializeNulls().
• Device override (local PreferencesRepository): shadows the account on this device only. Absent = follow the account, "auto" = pin to this device's clock, or a pinned IANA zone.

Resolution (device override > account > device-local) is exposed app-wide via a LocalDisplayTimeZone composition local, sourced from a cached account timezone (refreshed on login, persisted like file_cdn_base) combined with the local override.

UI

Settings → Appearance gains an Account timezone picker and an On this device override. Both use a searchable picker that leads with a "Common" group of friendly, DST-compensated names (Eastern Time (US & Canada), UK / Ireland (London), ...) then the full "All time zones" list, matching web's timezone-select. Selected common zones display their friendly label.

Applied

Front history, journal entry, and member-revision timestamps render in the resolved zone. This also fixes a latent bug where those journal/member times rendered in the server's offset (OffsetDateTime.toLocalDateTime()) rather than any chosen zone.

Scope / follow-up

Deliberately partial sweep. Remaining timestamp surfaces still render in the device clock and are tracked as follow-up: analytics grouping, poll close-dates, files, imports, retention, custom-field date editor, the history chart buckets + date-range pickers, the RecentFronts widget, and the Wear module. (Widget/wear are separate processes; the ViewModel surfaces need the effective zone via prefs rather than the composition local.)

Testing

• Unit tests for the resolver (tier precedence, auto, invalid-zone fallback) and the common-zone label mapping.
• :app:assemblePlayRelease green (through R8); unit suite green.
• Verified on device: account zone, device override, and history/journal/member times shifting.

Backend dependency

The account tier reads/writes System.timezone on /v1/systems/me, so it needs the timezone-enabled backend deployed to the target instance.