Replace thread latestTurnId with structured latestTurn metadata

- add `OrchestrationLatestTurn` schema and store full turn state/timestamps/message linkage
- update server projector/snapshot queries to populate `latestTurn` from session + projection_turns
- migrate web store/components to consume `latestTurn` and adjust related tests
4e3e689c5aJulius Marminge committed on 2/27/2026, 9:49:59 PMparent5b13d20
17 files changedLine totals unavailable