Represent persisted world state as JSON objects (#38274)

## Why

World-state snapshots and merge patches are keyed collections of sections. Allowing
their persisted `state` field to contain any JSON value required replay code to
handle shapes that cannot represent world state.

## What changed

- Type `WorldStateItem.state` and snapshot patches as JSON object maps.
- Reconstruct full snapshots directly from those maps and apply patches without
  fallible arbitrary-value conversions.
- Regenerate the app-server protocol schema for the object-only representation.

GitOrigin-RevId: 3d7662b74f3dd1f3ccc5fdd0200074c13a73cbe5

codex-rs/core/src/session/mod.rs

@@ -3362,7 +3362,7 @@ impl Session {
             state.replace_annotated_history(items, reference_context_item.clone());
             if let Some(world_state) = world_state_baseline {
                 let snapshot = world_state.snapshot();
-                world_state_item = Some(WorldStateItem::full(snapshot.clone().into_value()));
+                world_state_item = Some(WorldStateItem::full(snapshot.clone().into_object()));
                 state.history.set_world_state_baseline(snapshot);
             }
         }
@@ -3799,7 +3799,7 @@ impl Session {
                 .set_world_state_baseline(snapshot.clone());
             (
                 context_items,
-                Some(WorldStateItem::full(snapshot.into_value())),
+                Some(WorldStateItem::full(snapshot.into_object())),
             )
         } else {
             let (world_state_items, world_state_item) = {