- Core returns `InboundResult` — a typed struct with an optional
`NewConversation` and a `FrameOutcome` of decrypted messages.
- Client surfaces app-facing events via `Vec<Event>`, translated from
`InboundResult` at the boundary.
- MLS group welcomes now produce a `ConversationStarted` event with no
initial content, fixing the silent-group-join case where the inbox
layer dropped the observation.
- C FFI exposes an `EventList` opaque type with indexed accessors and
an `Invalid` sentinel for OOB / non-applicable reads.
- Symmetric `Inbox` / `InboxV2` handlers: both return
`Result<InboundResult, _>` and own the persistence + ephemeral-key
cleanup for the conversations they create.
- Updated and simplified `docs/adr/0001-client-event-system.md`.
