Simplify queued user message admission (#38092)

## What changed

- Resolve user message admission when Core accepts the input as a new turn or a steer, without waiting for rollout persistence.
- Remove persistence- and hook-specific admission errors and task bookkeeping.
- Delete queued messages after Core accepts them for turn processing, including messages subsequently stopped by a prompt hook.

## Testing

- Update concurrent admission and queue service tests for acceptance-based admission.

GitOrigin-RevId: 7dcc311cfecd3d710733b420f2add546edb86153

codex-rs/core/src/session/tests/guardian_tests.rs

@@ -463,7 +463,6 @@ async fn strict_auto_review_turn_grant_forces_guardian_for_shell_command_policy_
                 kind: crate::state::TaskKind::Regular,
                 listen_to_cancellation_token: true,
             },
-            /*input_persisted*/ None,
             crate::tasks::MailboxParentProvenance::Ignore,
         )
         .await;