Pass explicit render capabilities through App Render (#96576)
## Summary
`create-component-tree` currently combines `WorkStore.executionMode`
with route-level PPR configuration at several leaf call sites to
determine whether it can postpone dynamic subtrees and whether the
resulting response may be partial.
This introduces `AppRenderCapabilities`, derived once at the App Render
boundary, containing:
- `canPostpone`
- `isPossiblyPartialResponse`
- `supportsPerSegmentPrefetching`
Component tree construction consumes the explicit rendering capabilities
instead of independently interpreting the PPR configuration. RSC payload
generation likewise consumes `supportsPerSegmentPrefetching` instead of
re-deriving the client `S` flag from execution mode and Cache
Components, keeping the protocol decision consistent across dynamic,
initial, and error payloads.
