Offline: capture entries and transitions without a connection and sync them safely

Arnel, 14 September 2026: offline is one of the shapes a barako system should brew in, for a field worker without signal, a teacher's time in on a bad connection, or a registration desk when the venue's network drops.

## Change

- **Capture offline.** barakoPress pages (and the PWA module's app shell) can queue creates and named transitions in the browser when offline, each with a client-generated idempotency key (docs/idempotency.md) and the time it happened on the device.
- **Sync.** On reconnect the queue is sent in order. A write that the API now refuses (a validation, a uniqueness rule, a permission change) is shown to the user with the API's message to fix or discard, never silently dropped.
- **Conflicts.** Updates carry the version they were made against; a 412 is shown as "someone changed this while you were offline" with both values.
- **Device time.** The server records both the device time and the received time, so a time in captured offline at 7:58 is stored as 7:58, with the gap visible.
- **Read offline.** Pages and the lists a viewer may read are cached for offline reading with a clear "last updated" note.

## Done when

- A time in captured offline syncs once when the connection returns, keeps its device time, and a refused sync shows the reason.

## Where it lives

No core change. Offline capture and sync belong to barakoPress and the PWA module's service worker. The core already provides what sync needs: idempotency keys and versioned updates with If-Match.

Start with the barakoPress pages and the PWA module's service worker, then read docs/idempotency.md and the core's versioned-update and If-Match behavior. Trace how offline creates and named transitions can queue and replay in order, and define the cache and conflict paths. Done means an offline time-in syncs once with device time preserved, while refused writes and conflicts are shown to the user.

Written by the indexing model from the issue text.