Add Graveyard expiry warning and notification

[remdui]

What changed

• send a localized warning when an active or partially claimed grave enters its final 60 seconds
• send a localized message after the grave transitions to EXPIRED and disappears
• retry undelivered messages while the owner is offline, for as long as the grave remains in runtime retention
• avoid duplicate warnings and expiry messages
• reset the notification lifecycle when an expired grave is restored
• ignore already-expired records loaded from persistence so stale notifications are not emitted after startup
• add graveyard.expiry_warning and graveyard.expired localization keys
• bump Graveyard to 1.3.0

Implementation notes

A dedicated tracker observes immutable GraveSnapshot state rather than changing the durable claim and expiry transaction flow. This keeps notification failures isolated from grave persistence and prevents a chat-message issue from affecting expiry correctness.

Validation

• unit tests cover threshold behavior, retry-until-delivered semantics, one-shot expiry delivery, stale persisted records, and restored-grave cycles
• full repository CI and Paper acceptance checks are expected to run on this draft PR