Sender-side offline delivery hardening.
- OfferOutbox: a keystore-backed (no plaintext) queue of lot ids to publish
later. Stores ids, not offers, so on flush each offer is rebuilt from the
lot's CURRENT state — an offline edit is respected, a deleted lot drops out.
- flushOutbox(): on reconnect, republishes queued lots and clears them (no-op
offline; drops ids whose lot is gone).
- Market screen: sharing offline parks the lots ('we'll share these when you're
connected'); opening the market online auto-flushes the queue first.
- Wired via DI + TaneApp(outbox); i18n en/es/pt.
Tests: 4 outbox + 3 flush + market UI, 20 green. Analyzer clean for new code.